author | martin.trojer@nokia.com |
Fri, 31 Jul 2009 15:01:17 +0100 | |
changeset 1 | 2fb8b9db1c86 |
permissions | -rw-r--r-- |
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HOWTO Use Python in the web |
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******************************* |
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:Author: Marek Kubica |
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.. topic:: Abstract |
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This document shows how Python fits into the web. It presents some ways on |
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how to integrate Python with the web server and general practices useful for |
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developing web sites. |
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Programming for the Web has become a hot topic since the raise of the "Web 2.0", |
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which focuses on user-generated content on web sites. It has always been |
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possible to use Python for creating web sites, but it was a rather tedious task. |
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Therefore, many so-called "frameworks" and helper tools were created to help |
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developers creating sites faster and these sites being more robust. This HOWTO |
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describes some of the methods used to combine Python with a web server to create |
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dynamic content. It is not meant as a general introduction as this topic is far |
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too broad to be covered in one single document. However, a short overview of |
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the most popular libraries is provided. |
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.. seealso:: |
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While this HOWTO tries to give an overview over Python in the Web, it cannot |
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always be as up to date as desired. Web development in Python is moving |
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forward rapidly, so the wiki page on `Web Programming |
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<http://wiki.python.org/moin/WebProgramming>`_ might be more in sync with |
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recent development. |
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The low-level view |
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================== |
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.. .. image:: http.png |
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When a user enters a web site, his browser makes a connection to the site's |
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webserver (this is called the *request*). The server looks up the file in the |
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file system and sends it back to the user's browser, which displays it (this is |
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the *response*). This is roughly how the unterlying protocol, HTTP works. |
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Now, dynamic web sites are not files in the file system, but rather programs |
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which are run by the web server when a request comes in. They can do all sorts |
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of useful things, like display the postings of a bulletin board, show your |
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mails, configurate software or just display the current time. These programs |
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can be written in about any programming language the server supports, so it is |
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easy to use Python for creating dynamic web sites. |
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As most of HTTP servers are written in C or C++, they cannot execute Python code |
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in a simple way -- a bridge is needed between the server and the program. These |
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bridges or rather interfaces define how programs interact with the server. In |
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the past there have been numerous attempts to create the best possible |
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interface, but there are only a few worth mentioning. |
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Not every web server supports every interface. Many web servers do support only |
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old, now-obsolete interfaces. But they can often be extended using some |
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third-party modules to support new interfaces. |
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Common Gateway Interface |
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------------------------ |
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This interface is the oldest one, supported by nearly every web server out of |
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the box. Programs using CGI to communicate with their web server need to be |
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started by the server for every request. So, every request starts a new Python |
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interpreter -- which takes some time to start up -- thus making the whole |
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interface only usable for low load situations. |
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The upside of CGI is that it is simple -- writing a program which uses CGI is a |
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matter of about three lines of code. But this simplicity comes at a price: it |
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does very few things to help the developer. |
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Writing CGI programs, while still possible, is not recommended anymore. With |
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WSGI (more on that later) it is possible to write programs that emulate CGI, so |
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they can be run as CGI if no better option is available. |
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.. seealso:: |
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The Python standard library includes some modules that are helpful for |
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creating plain CGI programs: |
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* :mod:`cgi` -- Handling of user input in CGI scripts |
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* :mod:`cgitb` -- Displays nice tracebacks when errors happen in of CGI |
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applications, instead of presenting a "500 Internal Server Error" message |
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The Python wiki features a page on `CGI scripts |
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<http://wiki.python.org/moin/CgiScripts>`_ with some additional information |
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about CGI in Python. |
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Simple script for testing CGI |
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
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To test whether your web server works with CGI, you can use this short and |
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simple CGI program:: |
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#!/usr/bin/env python |
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# -*- coding: UTF-8 -*- |
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# enable debugging |
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import cgitb; cgitb.enable() |
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print "Content-Type: text/plain;charset=utf-8" |
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print "Hello World!" |
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|
108 |
|
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|
109 |
You need to write this code into a file with a ``.py`` or ``.cgi`` extension, |
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|
110 |
this depends on your web server configuration. Depending on your web server |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
111 |
configuration, this file may also need to be in a ``cgi-bin`` folder, for |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
112 |
security reasons. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
113 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
114 |
You might wonder what the ``cgitb`` line is about. This line makes it possible |
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|
115 |
to display a nice traceback instead of just crashing and displaying an "Internal |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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116 |
Server Error" in the user's browser. This is useful for debugging, but it might |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
117 |
risk exposing some confident data to the user. Don't use it when the script is |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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118 |
ready for production use. Still, you should *always* catch exceptions, and |
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119 |
display proper error pages -- end-users don't like to see nondescript "Internal |
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120 |
Server Errors" in their browsers. |
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121 |
|
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122 |
|
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123 |
Setting up CGI on your own server |
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124 |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
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125 |
|
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126 |
If you don't have your own web server, this does not apply to you. You can |
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127 |
check whether if works as-is and if not you need to talk to the administrator of |
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128 |
your web server anyway. If it is a big hoster, you can try filing a ticket |
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129 |
asking for Python support. |
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130 |
|
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131 |
If you're your own administrator or want to install it for testing purposes on |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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132 |
your own computers, you have to configure it by yourself. There is no one and |
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133 |
single way on how to configure CGI, as there are many web servers with different |
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134 |
configuration options. The currently most widely used free web server is |
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135 |
`Apache HTTPd <http://httpd.apache.org/>`_, Apache for short -- this is the one |
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136 |
that most people use, it can be easily installed on nearly every system using |
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137 |
the systems' package management. But `lighttpd <http://www.lighttpd.net>`_ has |
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138 |
been gaining attention since some time and is said to have a better performance. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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139 |
On many systems this server can also be installed using the package management, |
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140 |
so manually compiling the web server is never needed. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
141 |
|
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142 |
* On Apache you can take a look into the `Dynamic Content with CGI |
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143 |
<http://httpd.apache.org/docs/2.2/howto/cgi.html>`_ tutorial, where everything |
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144 |
is described. Most of the time it is enough just to set ``+ExecCGI``. The |
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145 |
tutorial also describes the most common gotchas that might arise. |
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146 |
* On lighttpd you need to use the `CGI module |
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147 |
<http://trac.lighttpd.net/trac/wiki/Docs%3AModCGI>`_ which can be configured |
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148 |
in a straightforward way. It boils down to setting ``cgi.assign`` properly. |
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|
149 |
|
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150 |
|
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151 |
Common problems with CGI scripts |
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152 |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
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|
153 |
|
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154 |
Trying to use CGI sometimes leads to small annoyances that one might experience |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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155 |
while trying to get these scripts to run. Sometimes it happens that a seemingly |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
156 |
correct script does not work as expected, which is caused by some small hidden |
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157 |
reason that's difficult to spot. |
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|
158 |
|
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|
159 |
Some of these reasons are: |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
160 |
|
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161 |
* The Python script is not marked executable. When CGI scripts are not |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
162 |
executable most of the web servers will let the user download it, instead of |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
163 |
running it and sending the output to the user. For CGI scripts to run |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
164 |
properly the ``+x`` bit needs to be set. Using ``chmod a+x your_script.py`` |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
165 |
might already solve the problem. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
166 |
* The line endings must be of Unix-type. This is important because the web |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
167 |
server checks the first line of the script (called shebang) and tries to run |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
168 |
the program specified there. It gets easily confused by Windows line endings |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
169 |
(Carriage Return & Line Feed, also called CRLF), so you have to convert the |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
170 |
file to Unix line endings (only Line Feed, LF). This can be done |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
171 |
automatically by uploading the file via FTP in text mode instead of binary |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
172 |
mode, but the preferred way is just telling your editor to save the files with |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
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|
173 |
Unix line endings. Most proper editors support this. |
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|
174 |
* Your web server must be able to read the file, you need to make sure the |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
175 |
permissions are fine. Often the server runs as user and group ``www-data``, |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
176 |
so it might be worth a try to change the file ownership or making the file |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
177 |
world readable by using ``chmod a+r your_script.py``. |
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|
178 |
* The webserver must be able to know that the file you're trying to access is a |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
179 |
CGI script. Check the configuration of your web server, maybe there is some |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
180 |
mistake. |
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|
181 |
* The path to the interpreter in the shebang (``#!/usr/bin/env python``) must be |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
182 |
currect. This line calls ``/usr/bin/env`` to find Python, but it'll fail if |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
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|
183 |
there is no ``/usr/bin/env``. If you know where your Python is installed, you |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
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|
184 |
can also use that path. The commands ``whereis python`` and ``type -p |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
185 |
python`` might also help to find where it is installed. Once this is known, |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
186 |
the shebang line can be changed accordingly: ``#!/usr/bin/python``. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
187 |
* The file must not contain a BOM (Byte Order Mark). The BOM is meant for |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
188 |
determining the byte order of UTF-16 encodings, but some editors write this |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
189 |
also into UTF-8 files. The BOM interferes with the shebang line, so be sure |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
190 |
to tell your editor not to write the BOM. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
191 |
* :ref:`mod-python` might be making problems. mod_python is able to handle CGI |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
192 |
scripts by itself, but it can also be a source for problems. Be sure you |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
193 |
disable it. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
194 |
|
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|
195 |
|
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|
196 |
.. _mod-python: |
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|
197 |
|
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|
198 |
mod_python |
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|
199 |
---------- |
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|
200 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
201 |
People coming from PHP often find it hard to grasp how to use Python in the web. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
202 |
Their first thought is mostly `mod_python <http://www.modpython.org/>`_ because |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
203 |
they think that this is the equivalent to ``mod_php``. Actually it is not |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
204 |
really. It does embed the interpreter into the Apache process, thus speeding up |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
205 |
requests by not having to start a Python interpreter every request. On the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
206 |
other hand, it is by far not "Python intermixed with HTML" as PHP often does. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
207 |
The Python equivalent of that is a template engine. mod_python itself is much |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
208 |
more powerful and gives more access to Apache internals. It can emulate CGI, it |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
209 |
can work an a "Python Server Pages" mode similar to JSP which is "HTML |
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intermangled with Python" and it has a "Publisher" which destignates one file to |
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accept all requests and decide on what to do then. |
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212 |
|
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But mod_python has some problems. Unlike the PHP interpreter the Python |
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interpreter uses caching when executing files, so when changing a file the whole |
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215 |
web server needs to be re-started to update. Another problem ist the basic |
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concept -- Apache starts some child processes to handle the requests and |
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unfortunately every child process needs to load the whole Python interpreter |
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even if it does not use it. This makes the whole web server slower. Another |
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219 |
problem is that as mod_python is linked against a specific version of |
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``libpython``, it is not possible to switch from an older version to a newer |
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(e.g. 2.4 to 2.5) without recompiling mod_python. mod_python is also bound to |
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the Apache web server, so programs written for mod_python cannot easily run on |
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223 |
other web servers. |
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224 |
|
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These are the reasons why mod_python should be avoided when writing new |
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programs. In some circumstances it might be still a good idea to use mod_python |
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for deployment, but WSGI makes it possible to run WSGI programs under mod_python |
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as well. |
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229 |
|
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230 |
|
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231 |
FastCGI and SCGI |
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232 |
---------------- |
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233 |
|
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FastCGI and SCGI try to solve the performance problem of CGI in another way. |
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Instead of embedding the interpreter into the web server, they create |
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long-running processes which run in the background. There still is some module |
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in the web server which makes it possible for the web server to "speak" with the |
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|
238 |
background process. As the background process is independent from the server, |
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239 |
it can be written in any language of course also in Python. The language just |
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needs to have a library which handles the communication with the web server. |
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|
241 |
|
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242 |
The difference between FastCGI and SCGI is very small, as SCGI is essentially |
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|
243 |
just a "simpler FastCGI". But as the web server support for SCGI is limited |
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most people use FastCGI instead, which works the same way. Almost everything |
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that applies to SCGI also applies to FastCGI as well, so we'll only write about |
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|
246 |
the latter. |
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|
247 |
|
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248 |
These days, FastCGI is never used directly. Just like ``mod_python`` it is only |
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|
249 |
used for the deployment of WSGI applications. |
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|
250 |
|
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251 |
.. seealso:: |
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|
252 |
|
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253 |
* `FastCGI, SCGI, and Apache: Background and Future |
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|
254 |
<http://www.vmunix.com/mark/blog/archives/2006/01/02/fastcgi-scgi-and-apache-background-and-future/>`_ |
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|
255 |
is a discussion on why the concept of FastCGI and SCGI is better that that |
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|
256 |
of mod_python. |
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|
257 |
|
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|
258 |
|
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|
259 |
Setting up FastCGI |
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|
260 |
^^^^^^^^^^^^^^^^^^ |
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|
261 |
|
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|
262 |
Depending on the web server you need to have a special module. |
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|
263 |
|
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|
264 |
* Apache has both `mod_fastcgi <http://www.fastcgi.com/>`_ and `mod_fcgid |
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|
265 |
<http://fastcgi.coremail.cn/>`_. ``mod_fastcgi`` is the original one, but it |
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|
266 |
has some licensing issues that's why it is sometimes considered non-free. |
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|
267 |
``mod_fcgid`` is a smaller, compatible alternative. One of these modules needs |
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|
268 |
to be loaded by Apache. |
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|
269 |
* lighttpd ships its own `FastCGI module |
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|
270 |
<http://trac.lighttpd.net/trac/wiki/Docs%3AModFastCGI>`_ as well as an `SCGI |
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|
271 |
module <http://trac.lighttpd.net/trac/wiki/Docs%3AModSCGI>`_. |
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|
272 |
* nginx also supports `FastCGI |
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|
273 |
<http://wiki.codemongers.com/NginxSimplePythonFCGI>`_. |
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|
274 |
|
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|
275 |
Once you have installed and configured the module, you can test it with the |
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|
276 |
following WSGI-application:: |
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|
277 |
|
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|
278 |
#!/usr/bin/env python |
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|
279 |
# -*- coding: UTF-8 -*- |
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|
280 |
|
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|
281 |
from cgi import escape |
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|
282 |
import sys, os |
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|
283 |
from flup.server.fcgi import WSGIServer |
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|
284 |
|
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|
285 |
def app(environ, start_response): |
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|
286 |
start_response('200 OK', [('Content-Type', 'text/html')]) |
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|
287 |
|
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|
288 |
yield '<h1>FastCGI Environment</h1>' |
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|
289 |
yield '<table>' |
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|
290 |
for k, v in sorted(environ.items()): |
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|
291 |
yield '<tr><th>%s</th><td>%s</td></tr>' % (escape(k), escape(v)) |
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|
292 |
yield '</table>' |
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|
293 |
|
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|
294 |
WSGIServer(app).run() |
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|
295 |
|
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|
296 |
This is a simple WSGI application, but you need to install `flup |
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|
297 |
<http://pypi.python.org/pypi/flup/1.0>`_ first, as flup handles the low level |
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|
298 |
FastCGI access. |
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|
299 |
|
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|
300 |
.. seealso:: |
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|
301 |
|
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|
302 |
There is some documentation on `setting up Django with FastCGI |
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|
303 |
<http://www.djangoproject.com/documentation/fastcgi/>`_, most of which can be |
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|
304 |
reused for other WSGI-compliant frameworks and libraries. Only the |
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|
305 |
``manage.py`` part has to be changed, the example used here can be used |
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|
306 |
instead. Django does more or less the exact same thing. |
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|
307 |
|
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|
308 |
|
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|
309 |
mod_wsgi |
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|
310 |
-------- |
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|
311 |
|
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|
312 |
`mod_wsgi <http://www.modwsgi.org/>`_ is an attempt to get rid of the low level |
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|
313 |
gateways. As FastCGI, SCGI, mod_python are mostly used to deploy WSGI |
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|
314 |
applications anyway, mod_wsgi was started to directly embed WSGI aplications |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
315 |
into the Apache web server. The benefit from this approach is that WSGI |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
316 |
applications can be deployed much easier as is is specially designed to host |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
317 |
WSGI applications -- unlike the other low level methods which have glue code to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
318 |
host WSGI applications (like flup which was mentioned before). The downside is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
319 |
that mod_wsgi is limited to the Apache web server, other servers would need |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
320 |
their own implementations of mod_wsgi. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
321 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
322 |
It supports two modes: the embedded mode in which it integrates with the Apache |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
323 |
process and the daemon mode which is more FastCGI-like. Contrary to FastCGI, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
324 |
mod_wsgi handles the worker-processes by itself which makes administration |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
325 |
easier. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
326 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
327 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
328 |
.. _WSGI: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
329 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
330 |
Step back: WSGI |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
331 |
=============== |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
332 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
333 |
WSGI was already mentioned several times so it has to be something important. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
334 |
In fact it really is, so now it's time to explain. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
335 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
336 |
The *Web Server Gateway Interface*, :pep:`333` or WSGI for short is currently |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
337 |
the best possible way to Python web programming. While it is great for |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
338 |
programmers writing frameworks, the normal person does not need to get in direct |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
339 |
contact with it. But when choosing a framework for web development it is a good |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
340 |
idea to take one which supports WSGI. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
341 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
342 |
The big profit from WSGI is the unification. When your program is compatible |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
343 |
with WSGI -- that means that your framework has support for WSGI, your program |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
344 |
can be deployed on every web server interface for which there are WSGI wrappers. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
345 |
So you do not need to care about whether the user uses mod_python or FastCGI -- |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
346 |
with WSGI it just works on any gateway interface. The Python standard library |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
347 |
contains its own WSGI server :mod:`wsgiref`, which is a small web server that |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
348 |
can be used for testing. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
349 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
350 |
A really great WSGI feature are the middlewares. Middlewares are layers around |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
351 |
your program which can add various functionality to it. There is a `number of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
352 |
middlewares <http://wsgi.org/wsgi/Middleware_and_Utilities>`_ already available. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
353 |
For example, instead of writing your own session management (to identify a user |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
354 |
in subsequent requests, as HTTP does not maintain state, so it does now know |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
355 |
that the requests belong to the same user) you can just take one middleware, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
356 |
plug it in and you can rely an already existing functionality. The same thing |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
357 |
is compression -- say you want to compress your HTML using gzip, to save your |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
358 |
server's bandwidth. So you only need to plug-in a middleware and you're done. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
359 |
Authentication is also a problem easily solved using a middleware. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
360 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
361 |
So, generally -- although WSGI may seem complex, the initial phase of learning |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
362 |
can be very rewarding as WSGI does already have solutions to many problems that |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
363 |
might arise while writing web sites. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
364 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
365 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
366 |
WSGI Servers |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
367 |
------------ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
368 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
369 |
The code that is used to connect to various low level gateways like CGI or |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
370 |
mod_python is called *WSGI server*. One of these servers is ``flup`` which was |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
371 |
already mentioned and supports FastCGI, SCGI as well as `AJP |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
372 |
<http://en.wikipedia.org/wiki/Apache_JServ_Protocol>`_. Some of these servers |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
373 |
are written in Python as ``flup`` is, but there also exist others which are |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
374 |
written in C and can be used as drop-in replacements. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
375 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
376 |
There are quite a lot of servers already available, so a Python web application |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
377 |
can be deployed nearly everywhere. This is one big advantage that Python has |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
378 |
compared with other web techniques. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
379 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
380 |
.. seealso:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
381 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
382 |
A good overview of all WSGI-related code can be found in the `WSGI wiki |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
383 |
<http://wsgi.org/wsgi>`_, which contains an extensive list of `WSGI servers |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
384 |
<http://wsgi.org/wsgi/Servers>`_, which can be used by *every* application |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
385 |
supporting WSGI. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
386 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
387 |
You might be interested in some WSGI-supporting modules already contained in |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
388 |
the standard library, namely: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
389 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
390 |
* :mod:`wsgiref` -- some tiny utilities and servers for WSGI |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
391 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
392 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
393 |
Case study: MoinMoin |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
394 |
-------------------- |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
395 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
396 |
What does WSGI give the web application developer? Let's take a look on one |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
397 |
long existing web application written in Python without using WSGI. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
398 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
399 |
One of the most widely used wiki software is `MoinMoin <http://moinmo.in/>`_. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
400 |
It was created in 2000, so it predates WSGI by about three years. While it now |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
401 |
includes support for WSGI, older versions needed separate code to run on CGI, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
402 |
mod_python, FastCGI and standalone. Now, this all is possible by using WSGI and |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
403 |
the already-written gateways. For running with on FastCGI ``flup`` can be used, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
404 |
for running a standalone server :mod:`wsgiref` is the way to go. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
405 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
406 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
407 |
Model-view-controller |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
408 |
===================== |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
409 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
410 |
The term *MVC* is often heard in statements like "framework *foo* supports MVC". |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
411 |
While MVC is not really something technical but rather organisational, many web |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
412 |
frameworks use this model to help the developer to bring structure into his |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
413 |
program. Bigger web applications can have lots of code so it is a good idea to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
414 |
have structure in the program right from the beginnings. That way, even users |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
415 |
of other frameworks (or even languages, as MVC is nothing Python-specific) can |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
416 |
understand the existing code easier, as they are already familiar with the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
417 |
structure. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
418 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
419 |
MVC stands for three components: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
420 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
421 |
* The *model*. This is the data that is meant to modify. In Python frameworks |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
422 |
this component is often represented by the classes used by the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
423 |
object-relational mapper. So, all declarations go here. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
424 |
* The *view*. This component's job is to display the data of the model to the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
425 |
user. Typically this component is represented by the templates. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
426 |
* The *controller*. This is the layer between the user and the model. The |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
427 |
controller reacts on user actions (like opening some specific URL) and tells |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
428 |
the model to modify the data if neccessary. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
429 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
430 |
While one might think that MVC is a complex design pattern, in fact it is not. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
431 |
It is used in Python because it has turned out to be useful for creating clean, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
432 |
maintainable web sites. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
433 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
434 |
.. note:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
435 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
436 |
While not all Python frameworks explicitly support MVC, it is often trivial |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
437 |
to create a web site which uses the MVC pattern by seperating the data logic |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
438 |
(the model) from the user interaction logic (the controller) and the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
439 |
templates (the view). That's why it is important not to write unneccessary |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
440 |
Python code in the templates -- it is against MVC and creates more chaos. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
441 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
442 |
.. seealso:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
443 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
444 |
The english Wikipedia has an article about the `Model-View-Controller pattern |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
445 |
<http://en.wikipedia.org/wiki/Model-view-controller>`_, which includes a long |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
446 |
list of web frameworks for different programming languages. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
447 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
448 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
449 |
Ingredients for web sites |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
450 |
========================= |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
451 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
452 |
Web sites are complex constructs, so tools were created to help the web site |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
453 |
developer to make his work maintainable. None of these tools are in any way |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
454 |
Python specific, they also exist for other programming languages as well. Of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
455 |
course, developers are not forced to use these tools and often there is no |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
456 |
"best" tool, but it is worth informing yourself before choosing something |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
457 |
because of the big number of helpers that the developer can use. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
458 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
459 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
460 |
.. seealso:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
461 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
462 |
People have written far more components that can be combined than these |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
463 |
presented here. The Python wiki has a page about these components, called |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
464 |
`Web Components <http://wiki.python.org/moin/WebComponents>`_. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
465 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
466 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
467 |
Templates |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
468 |
--------- |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
469 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
470 |
Mixing of HTML and Python code is possible with some libraries. While |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
471 |
convenient at first, it leads to horribly unmaintainable code. That's why |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
472 |
templates exist. Templates are, in the simplest case, just HTML files with |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
473 |
placeholders. The HTML is sent to the user's browser after filling out the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
474 |
placeholders. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
475 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
476 |
Python already includes such simple templates:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
477 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
478 |
# a simple template |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
479 |
template = "<html><body><h1>Hello %s!</h1></body></html>" |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
480 |
print template % "Reader" |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
481 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
482 |
The Python standard library also includes some more advanced templates usable |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
483 |
through :class:`string.Template`, but in HTML templates it is needed to use |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
484 |
conditional and looping contructs like Python's *for* and *if*. So, some |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
485 |
*template engine* is needed. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
486 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
487 |
Now, Python has a lot of template engines which can be used with or without a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
488 |
`framework`_. Some of these are using a plain-text programming language which |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
489 |
is very easy to learn as it is quite limited while others use XML so the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
490 |
template output is always guaranteed to be valid XML. Some `frameworks`_ ship |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
491 |
their own template engine or recommend one particular. If one is not yet sure, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
492 |
using these is a good idea. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
493 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
494 |
.. note:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
495 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
496 |
While Python has quite a lot of different template engines it usually does |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
497 |
not make sense to use a homebrewed template system. The time needed to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
498 |
evaluate all templating systems is not really worth it, better invest the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
499 |
time in looking through the most popular ones. Some frameworks have their |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
500 |
own template engine or have a recommentation for one. It's wise to use |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
501 |
these. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
502 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
503 |
Popular template engines include: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
504 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
505 |
* Mako |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
506 |
* Genshi |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
507 |
* Jinja |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
508 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
509 |
.. seealso:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
510 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
511 |
Lots of different template engines divide the attention between themselves |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
512 |
because it's easy to create them in Python. The page `Templating |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
513 |
<http://wiki.python.org/moin/Templating>`_ in the wiki lists a big, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
514 |
ever-growing number of these. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
515 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
516 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
517 |
Data persistence |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
518 |
---------------- |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
519 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
520 |
*Data persistence*, while sounding very complicated is just about storing data. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
521 |
This data might be the text of blog entries, the postings of a bulletin board or |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
522 |
the text of a wiki page. As always, there are different ways to store |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
523 |
informations on a web server. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
524 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
525 |
Often relational database engines like `MySQL <http://www.mysql.com/>`_ or |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
526 |
`PostgreSQL <http://http://www.postgresql.org/>`_ are used due to their good |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
527 |
performance handling very large databases consisting of up to millions of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
528 |
entries. These are *queried* using a language called `SQL |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
529 |
<http://en.wikipedia.org/wiki/SQL>`_. Python programmers in general do not like |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
530 |
SQL too much, they prefer to work with objects. It is possible to save Python |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
531 |
objects into a database using a technology called `ORM |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
532 |
<http://en.wikipedia.org/wiki/Object-relational_mapping>`_. ORM translates all |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
533 |
object-oriented access into SQL code under the hood, the user does not need to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
534 |
think about it. Most `frameworks`_ use ORMs and it works quite well. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
535 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
536 |
A second possibility is using files that are saved on the hard disk (sometimes |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
537 |
called flatfiles). This is very easy, but is not too fast. There is even a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
538 |
small database engine called `SQLite <http://www.sqlite.org/>`_ which is bundled |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
539 |
with Python in the :mod:`sqlite` module and uses only one file. This database |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
540 |
can be used to store objects via an ORM and has no other dependencies. For |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
541 |
smaller sites SQLite is just enough. But it is not the only way in which data |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
542 |
can be saved into the file systems. Sometimes normal, plain text files are |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
543 |
enough. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
544 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
545 |
The third and least used possibility are so-called object oriented databases. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
546 |
These databases store the *actual objects* instead of the relations that |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
547 |
OR-mapping creates between rows in a database. This has the advantage that |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
548 |
nearly all objects can be saven in a straightforward way, unlike in relational |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
549 |
databases where some objects are very hard to represent with ORMs. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
550 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
551 |
`Frameworks`_ often give the users hints on which method to choose, it is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
552 |
usually a good idea to stick to these unless there are some special requirements |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
553 |
which require to use the one method and not the other. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
554 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
555 |
.. seealso:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
556 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
557 |
* `Persistence Tools <http://wiki.python.org/moin/PersistenceTools>`_ lists |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
558 |
possibilities on how to save data in the file system, some of these modules |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
559 |
are part of the standard library |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
560 |
* `Database Programming <http://wiki.python.org/moin/DatabaseProgramming>`_ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
561 |
helps on choosing a method on how to save the data |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
562 |
* `SQLAlchemy <http://www.sqlalchemy.org/>`_, the most powerful OR-Mapper for |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
563 |
Python and `Elixir <http://elixir.ematia.de/>`_ which makes it easier to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
564 |
use |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
565 |
* `SQLObject <http://www.sqlobject.org/>`_, another popular OR-Mapper |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
566 |
* `ZODB <https://launchpad.net/zodb>`_ and `Durus |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
567 |
<http://www.mems-exchange.org/software/durus/>`_, two object oriented |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
568 |
databases |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
569 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
570 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
571 |
.. _framework: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
572 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
573 |
Frameworks |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
574 |
========== |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
575 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
576 |
As web sites can easily become quite large, there are so-called frameworks which |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
577 |
were created to help the developer with making these sites. Although the most |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
578 |
well-known framework is Ruby on Rails, Python does also have its own frameworks |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
579 |
which are partly inspired by Rails or which were existing a long time before |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
580 |
Rails. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
581 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
582 |
Two possible approaches to web frameworks exist: the minimalistic approach and |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
583 |
the all-inclusive approach (somtimes called *full-stack*). Frameworks which are |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
584 |
all-inclusive give you everything you need to start working, like a template |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
585 |
engine, some way to save and access data in databases and many features more. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
586 |
Most users are best off using these as they are widely used by lots of other |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
587 |
users and well documented in form of books and tutorials. Other web frameworks |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
588 |
go the minimalistic approach trying to be as flexible as possible leaving the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
589 |
user the freedom to choose what's best for him. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
590 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
591 |
The majority of users is best off with all-inclusive framewors. They bring |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
592 |
everything along so a user can just jump in and start to code. While they do |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
593 |
have some limitations they can fullfill 80% of what one will ever want to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
594 |
perfectly. They consist of various components which are designed to work |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
595 |
together as good as possible. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
596 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
597 |
The multitude of web frameworks written in Python demonstrates that it is really |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
598 |
easy to write one. One of the most well-known web applications written in |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
599 |
Python is `Zope <http://www.zope.org/>`_ which can be regarded as some kind of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
600 |
big framework. But Zope was not the only framework, there were some others |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
601 |
which are by now nearly forgotten. These do not need to be mentioned anymore, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
602 |
because most people that used them moved on to newer ones. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
603 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
604 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
605 |
Some notable frameworks |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
606 |
----------------------- |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
607 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
608 |
There is an incredible number of frameworks, so there is no way to describe them |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
609 |
all. It is not even neccessary, as most of these frameworks are nothing special |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
610 |
and everything that can be done with these can also be done with one of the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
611 |
popular ones. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
612 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
613 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
614 |
Django |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
615 |
^^^^^^ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
616 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
617 |
`Django <http://www.djangoproject.com/>`_ is a framework consisting of several |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
618 |
tightly coupled elements which were written from scratch and work together very |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
619 |
well. It includes an ORM which is quite powerful while being simple to use and |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
620 |
has a great online administration interface which makes it possible to edit the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
621 |
data in the database with a browser. The template engine is text-based and is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
622 |
designed to be usable for page designers who cannot write Python. It supports |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
623 |
so-called template inheritance and filters (which work like Unix pipes). Django |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
624 |
has many handy features bundled, like creation of RSS feeds or generic views |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
625 |
which make it possible to write web sites nearly without any Python code. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
626 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
627 |
It has a big, international community which has created many sites using Django. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
628 |
There are also quite a lot of add-on projects which extend Django's normal |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
629 |
functionality. This is partly due to Django's well written `online |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
630 |
documentation <http://doc.djangoproject.com/>`_ and the `Django book |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
631 |
<http://www.djangobook.com/>`_. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
632 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
633 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
634 |
.. note:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
635 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
636 |
Although Django is an MVC-style framework, it calls the components |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
637 |
differently, which is described in the `Django FAQ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
638 |
<http://www.djangoproject.com/documentation/faq/#django-appears-to-be-a-mvc-framework-but-you-call-the-controller-the-view-and-the-view-the-template-how-come-you-don-t-use-the-standard-names>`_. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
639 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
640 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
641 |
TurboGears |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
642 |
^^^^^^^^^^ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
643 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
644 |
The other popular web framework in Python is `TurboGears |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
645 |
<http://www.turbogears.org/>`_. It takes the approach of using already existing |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
646 |
components and combining them with glue code to create a seamless experience. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
647 |
TurboGears gives the user more flexibility on which components to choose, the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
648 |
ORM can be switched between some easy to use but limited and complex but very |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
649 |
powerful. Same goes for the template engine. One strong point about TurboGears |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
650 |
is that the components that it consists of can be used easily in other projects |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
651 |
without depending on TurboGears, for example the underlying web server CherryPy. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
652 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
653 |
The documentation can be found in the `TurboGears wiki |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
654 |
<http://docs.turbogears.org/>`_, where links to screencasts can be found. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
655 |
TurboGears has also an active user community which can respond to most related |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
656 |
questions. There is also a `TurboGears book <http://turbogearsbook.com/>`_ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
657 |
published, which is a good starting point. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
658 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
659 |
The plan for the next major version of TurboGears, version 2.0 is to switch to a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
660 |
more flexible base provided by another very flexible web framework called |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
661 |
`Pylons <http://pylonshq.com/>`_. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
662 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
663 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
664 |
Other notable frameworks |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
665 |
^^^^^^^^^^^^^^^^^^^^^^^^ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
666 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
667 |
These two are of course not the only frameworks that are available, there are |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
668 |
also some less-popular frameworks worth mentioning. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
669 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
670 |
One of these is the already mentioned Zope, which has been around for quite a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
671 |
long time. With Zope 2.x having been known as rather un-pythonic, the newer |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
672 |
Zope 3.x tries to change that and therefore gets more acceptance from Python |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
673 |
programmers. These efforts already showed results, there is a project which |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
674 |
connects Zope with WSGI called `Repoze <http://repoze.org/>`_ and another |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
675 |
project called `Grok <http://grok.zope.org/>`_ which makes it possible for |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
676 |
"normal" Python programmers use the very mature Zope components. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
677 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
678 |
Another framework that's already been mentioned is `Pylons`_. Pylons is much |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
679 |
like TurboGears with ab even stronger emphasis on flexibility, which is bought |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
680 |
at the cost of being more difficult to use. Nearly every component can be |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
681 |
exchanged, which makes it neccessary to use the documentation of every single |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
682 |
component, because there are so many Pylons combinations possible that can |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
683 |
satisfy every requirement. Pylons builds upon `Paste |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
684 |
<http://pythonpaste.org/>`_, an extensive set of tools which are handy for WSGI. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
685 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
686 |
And that's still not everything. The most up-to-date information can always be |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
687 |
found in the Python wiki. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
688 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
689 |
.. seealso:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
690 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
691 |
The Python wiki contains an extensive list of `web frameworks |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
692 |
<http://wiki.python.org/moin/WebFrameworks>`_. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
693 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
694 |
Most frameworks also have their own mailing lists and IRC channels, look out |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
695 |
for these on the projects' websites. There is also a general "Python in the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
696 |
Web" IRC channel on freenode called `#python.web |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
697 |
<http://wiki.python.org/moin/PoundPythonWeb>`_. |