author | martin.trojer@nokia.com |
Fri, 31 Jul 2009 15:01:17 +0100 | |
changeset 1 | 2fb8b9db1c86 |
permissions | -rw-r--r-- |
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.. _tut-modules: |
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******* |
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Modules |
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******* |
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If you quit from the Python interpreter and enter it again, the definitions you |
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have made (functions and variables) are lost. Therefore, if you want to write a |
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somewhat longer program, you are better off using a text editor to prepare the |
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input for the interpreter and running it with that file as input instead. This |
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is known as creating a *script*. As your program gets longer, you may want to |
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split it into several files for easier maintenance. You may also want to use a |
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handy function that you've written in several programs without copying its |
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definition into each program. |
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To support this, Python has a way to put definitions in a file and use them in a |
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script or in an interactive instance of the interpreter. Such a file is called a |
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*module*; definitions from a module can be *imported* into other modules or into |
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the *main* module (the collection of variables that you have access to in a |
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script executed at the top level and in calculator mode). |
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A module is a file containing Python definitions and statements. The file name |
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is the module name with the suffix :file:`.py` appended. Within a module, the |
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module's name (as a string) is available as the value of the global variable |
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``__name__``. For instance, use your favorite text editor to create a file |
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called :file:`fibo.py` in the current directory with the following contents:: |
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# Fibonacci numbers module |
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def fib(n): # write Fibonacci series up to n |
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a, b = 0, 1 |
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while b < n: |
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print b, |
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a, b = b, a+b |
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def fib2(n): # return Fibonacci series up to n |
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result = [] |
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a, b = 0, 1 |
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while b < n: |
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result.append(b) |
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a, b = b, a+b |
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return result |
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Now enter the Python interpreter and import this module with the following |
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command:: |
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>>> import fibo |
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This does not enter the names of the functions defined in ``fibo`` directly in |
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the current symbol table; it only enters the module name ``fibo`` there. Using |
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the module name you can access the functions:: |
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>>> fibo.fib(1000) |
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1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 |
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>>> fibo.fib2(100) |
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[1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89] |
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>>> fibo.__name__ |
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'fibo' |
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If you intend to use a function often you can assign it to a local name:: |
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>>> fib = fibo.fib |
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>>> fib(500) |
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.. _tut-moremodules: |
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More on Modules |
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=============== |
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A module can contain executable statements as well as function definitions. |
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These statements are intended to initialize the module. They are executed only |
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the *first* time the module is imported somewhere. [#]_ |
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Each module has its own private symbol table, which is used as the global symbol |
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table by all functions defined in the module. Thus, the author of a module can |
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use global variables in the module without worrying about accidental clashes |
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with a user's global variables. On the other hand, if you know what you are |
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doing you can touch a module's global variables with the same notation used to |
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refer to its functions, ``modname.itemname``. |
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Modules can import other modules. It is customary but not required to place all |
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:keyword:`import` statements at the beginning of a module (or script, for that |
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matter). The imported module names are placed in the importing module's global |
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symbol table. |
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There is a variant of the :keyword:`import` statement that imports names from a |
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module directly into the importing module's symbol table. For example:: |
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>>> from fibo import fib, fib2 |
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>>> fib(500) |
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This does not introduce the module name from which the imports are taken in the |
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local symbol table (so in the example, ``fibo`` is not defined). |
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There is even a variant to import all names that a module defines:: |
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>>> from fibo import * |
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>>> fib(500) |
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This imports all names except those beginning with an underscore (``_``). |
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.. note:: |
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For efficiency reasons, each module is only imported once per interpreter |
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session. Therefore, if you change your modules, you must restart the |
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interpreter -- or, if it's just one module you want to test interactively, |
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use :func:`reload`, e.g. ``reload(modulename)``. |
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112 |
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113 |
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.. _tut-modulesasscripts: |
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115 |
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Executing modules as scripts |
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---------------------------- |
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118 |
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When you run a Python module with :: |
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120 |
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python fibo.py <arguments> |
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122 |
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the code in the module will be executed, just as if you imported it, but with |
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the ``__name__`` set to ``"__main__"``. That means that by adding this code at |
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the end of your module:: |
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126 |
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if __name__ == "__main__": |
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import sys |
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fib(int(sys.argv[1])) |
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130 |
|
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you can make the file usable as a script as well as an importable module, |
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because the code that parses the command line only runs if the module is |
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executed as the "main" file:: |
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134 |
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$ python fibo.py 50 |
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136 |
1 1 2 3 5 8 13 21 34 |
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137 |
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If the module is imported, the code is not run:: |
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139 |
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>>> import fibo |
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>>> |
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142 |
|
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This is often used either to provide a convenient user interface to a module, or |
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for testing purposes (running the module as a script executes a test suite). |
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145 |
|
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146 |
|
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.. _tut-searchpath: |
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148 |
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149 |
The Module Search Path |
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150 |
---------------------- |
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151 |
|
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.. index:: triple: module; search; path |
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153 |
|
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When a module named :mod:`spam` is imported, the interpreter searches for a file |
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named :file:`spam.py` in the current directory, and then in the list of |
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directories specified by the environment variable :envvar:`PYTHONPATH`. This |
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has the same syntax as the shell variable :envvar:`PATH`, that is, a list of |
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158 |
directory names. When :envvar:`PYTHONPATH` is not set, or when the file is not |
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found there, the search continues in an installation-dependent default path; on |
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Unix, this is usually :file:`.:/usr/local/lib/python`. |
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161 |
|
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Actually, modules are searched in the list of directories given by the variable |
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``sys.path`` which is initialized from the directory containing the input script |
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(or the current directory), :envvar:`PYTHONPATH` and the installation- dependent |
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default. This allows Python programs that know what they're doing to modify or |
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166 |
replace the module search path. Note that because the directory containing the |
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script being run is on the search path, it is important that the script not have |
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the same name as a standard module, or Python will attempt to load the script as |
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169 |
a module when that module is imported. This will generally be an error. See |
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section :ref:`tut-standardmodules` for more information. |
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171 |
|
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172 |
|
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"Compiled" Python files |
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174 |
----------------------- |
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175 |
|
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176 |
As an important speed-up of the start-up time for short programs that use a lot |
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177 |
of standard modules, if a file called :file:`spam.pyc` exists in the directory |
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where :file:`spam.py` is found, this is assumed to contain an |
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already-"byte-compiled" version of the module :mod:`spam`. The modification time |
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of the version of :file:`spam.py` used to create :file:`spam.pyc` is recorded in |
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:file:`spam.pyc`, and the :file:`.pyc` file is ignored if these don't match. |
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182 |
|
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183 |
Normally, you don't need to do anything to create the :file:`spam.pyc` file. |
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184 |
Whenever :file:`spam.py` is successfully compiled, an attempt is made to write |
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185 |
the compiled version to :file:`spam.pyc`. It is not an error if this attempt |
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186 |
fails; if for any reason the file is not written completely, the resulting |
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:file:`spam.pyc` file will be recognized as invalid and thus ignored later. The |
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188 |
contents of the :file:`spam.pyc` file are platform independent, so a Python |
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189 |
module directory can be shared by machines of different architectures. |
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190 |
|
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191 |
Some tips for experts: |
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192 |
|
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193 |
* When the Python interpreter is invoked with the :option:`-O` flag, optimized |
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code is generated and stored in :file:`.pyo` files. The optimizer currently |
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195 |
doesn't help much; it only removes :keyword:`assert` statements. When |
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:option:`-O` is used, *all* :term:`bytecode` is optimized; ``.pyc`` files are |
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ignored and ``.py`` files are compiled to optimized bytecode. |
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198 |
|
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* Passing two :option:`-O` flags to the Python interpreter (:option:`-OO`) will |
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cause the bytecode compiler to perform optimizations that could in some rare |
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201 |
cases result in malfunctioning programs. Currently only ``__doc__`` strings are |
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removed from the bytecode, resulting in more compact :file:`.pyo` files. Since |
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some programs may rely on having these available, you should only use this |
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option if you know what you're doing. |
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205 |
|
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* A program doesn't run any faster when it is read from a :file:`.pyc` or |
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:file:`.pyo` file than when it is read from a :file:`.py` file; the only thing |
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that's faster about :file:`.pyc` or :file:`.pyo` files is the speed with which |
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they are loaded. |
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210 |
|
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* When a script is run by giving its name on the command line, the bytecode for |
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the script is never written to a :file:`.pyc` or :file:`.pyo` file. Thus, the |
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startup time of a script may be reduced by moving most of its code to a module |
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and having a small bootstrap script that imports that module. It is also |
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possible to name a :file:`.pyc` or :file:`.pyo` file directly on the command |
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line. |
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* It is possible to have a file called :file:`spam.pyc` (or :file:`spam.pyo` |
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when :option:`-O` is used) without a file :file:`spam.py` for the same module. |
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This can be used to distribute a library of Python code in a form that is |
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moderately hard to reverse engineer. |
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.. index:: module: compileall |
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* The module :mod:`compileall` can create :file:`.pyc` files (or :file:`.pyo` |
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files when :option:`-O` is used) for all modules in a directory. |
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.. _tut-standardmodules: |
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Standard Modules |
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================ |
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.. index:: module: sys |
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Python comes with a library of standard modules, described in a separate |
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document, the Python Library Reference ("Library Reference" hereafter). Some |
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modules are built into the interpreter; these provide access to operations that |
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are not part of the core of the language but are nevertheless built in, either |
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for efficiency or to provide access to operating system primitives such as |
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system calls. The set of such modules is a configuration option which also |
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depends on the underlying platform For example, the :mod:`winreg` module is only |
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provided on Windows systems. One particular module deserves some attention: |
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:mod:`sys`, which is built into every Python interpreter. The variables |
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``sys.ps1`` and ``sys.ps2`` define the strings used as primary and secondary |
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prompts:: |
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|
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>>> import sys |
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>>> sys.ps1 |
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'>>> ' |
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>>> sys.ps2 |
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'... ' |
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>>> sys.ps1 = 'C> ' |
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C> print 'Yuck!' |
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Yuck! |
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C> |
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These two variables are only defined if the interpreter is in interactive mode. |
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The variable ``sys.path`` is a list of strings that determines the interpreter's |
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search path for modules. It is initialized to a default path taken from the |
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environment variable :envvar:`PYTHONPATH`, or from a built-in default if |
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:envvar:`PYTHONPATH` is not set. You can modify it using standard list |
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operations:: |
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|
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>>> import sys |
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>>> sys.path.append('/ufs/guido/lib/python') |
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|
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|
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.. _tut-dir: |
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|
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The :func:`dir` Function |
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======================== |
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|
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The built-in function :func:`dir` is used to find out which names a module |
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defines. It returns a sorted list of strings:: |
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|
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>>> import fibo, sys |
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>>> dir(fibo) |
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['__name__', 'fib', 'fib2'] |
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>>> dir(sys) |
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['__displayhook__', '__doc__', '__excepthook__', '__name__', '__stderr__', |
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'__stdin__', '__stdout__', '_getframe', 'api_version', 'argv', |
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'builtin_module_names', 'byteorder', 'callstats', 'copyright', |
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'displayhook', 'exc_clear', 'exc_info', 'exc_type', 'excepthook', |
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'exec_prefix', 'executable', 'exit', 'getdefaultencoding', 'getdlopenflags', |
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'getrecursionlimit', 'getrefcount', 'hexversion', 'maxint', 'maxunicode', |
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'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_cache', |
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'platform', 'prefix', 'ps1', 'ps2', 'setcheckinterval', 'setdlopenflags', |
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'setprofile', 'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout', |
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'version', 'version_info', 'warnoptions'] |
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|
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Without arguments, :func:`dir` lists the names you have defined currently:: |
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|
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>>> a = [1, 2, 3, 4, 5] |
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>>> import fibo |
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>>> fib = fibo.fib |
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>>> dir() |
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['__builtins__', '__doc__', '__file__', '__name__', 'a', 'fib', 'fibo', 'sys'] |
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|
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Note that it lists all types of names: variables, modules, functions, etc. |
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|
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.. index:: module: __builtin__ |
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|
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:func:`dir` does not list the names of built-in functions and variables. If you |
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want a list of those, they are defined in the standard module |
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:mod:`__builtin__`:: |
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|
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>>> import __builtin__ |
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>>> dir(__builtin__) |
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['ArithmeticError', 'AssertionError', 'AttributeError', 'DeprecationWarning', |
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'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', |
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'FloatingPointError', 'FutureWarning', 'IOError', 'ImportError', |
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'IndentationError', 'IndexError', 'KeyError', 'KeyboardInterrupt', |
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'LookupError', 'MemoryError', 'NameError', 'None', 'NotImplemented', |
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'NotImplementedError', 'OSError', 'OverflowError', |
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318 |
'PendingDeprecationWarning', 'ReferenceError', 'RuntimeError', |
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|
319 |
'RuntimeWarning', 'StandardError', 'StopIteration', 'SyntaxError', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
320 |
'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'True', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
321 |
'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
322 |
'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
323 |
'UserWarning', 'ValueError', 'Warning', 'WindowsError', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
324 |
'ZeroDivisionError', '_', '__debug__', '__doc__', '__import__', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
325 |
'__name__', 'abs', 'apply', 'basestring', 'bool', 'buffer', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
326 |
'callable', 'chr', 'classmethod', 'cmp', 'coerce', 'compile', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
327 |
'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
328 |
'enumerate', 'eval', 'execfile', 'exit', 'file', 'filter', 'float', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
329 |
'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
330 |
'id', 'input', 'int', 'intern', 'isinstance', 'issubclass', 'iter', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
331 |
'len', 'license', 'list', 'locals', 'long', 'map', 'max', 'min', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
332 |
'object', 'oct', 'open', 'ord', 'pow', 'property', 'quit', 'range', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
333 |
'raw_input', 'reduce', 'reload', 'repr', 'reversed', 'round', 'set', |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
334 |
'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
335 |
'tuple', 'type', 'unichr', 'unicode', 'vars', 'xrange', 'zip'] |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
336 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
337 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
338 |
.. _tut-packages: |
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|
339 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
340 |
Packages |
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|
341 |
======== |
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
342 |
|
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Initial QEMU (symbian-qemu-0.9.1-12) import
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|
343 |
Packages are a way of structuring Python's module namespace by using "dotted |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
344 |
module names". For example, the module name :mod:`A.B` designates a submodule |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
345 |
named ``B`` in a package named ``A``. Just like the use of modules saves the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
346 |
authors of different modules from having to worry about each other's global |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
347 |
variable names, the use of dotted module names saves the authors of multi-module |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
348 |
packages like NumPy or the Python Imaging Library from having to worry about |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
349 |
each other's module names. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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|
350 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
351 |
Suppose you want to design a collection of modules (a "package") for the uniform |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
352 |
handling of sound files and sound data. There are many different sound file |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
353 |
formats (usually recognized by their extension, for example: :file:`.wav`, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
354 |
:file:`.aiff`, :file:`.au`), so you may need to create and maintain a growing |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
355 |
collection of modules for the conversion between the various file formats. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
356 |
There are also many different operations you might want to perform on sound data |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
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|
357 |
(such as mixing, adding echo, applying an equalizer function, creating an |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
358 |
artificial stereo effect), so in addition you will be writing a never-ending |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
359 |
stream of modules to perform these operations. Here's a possible structure for |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
360 |
your package (expressed in terms of a hierarchical filesystem):: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
361 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
362 |
sound/ Top-level package |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
363 |
__init__.py Initialize the sound package |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
364 |
formats/ Subpackage for file format conversions |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
365 |
__init__.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
366 |
wavread.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
367 |
wavwrite.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
368 |
aiffread.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
369 |
aiffwrite.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
370 |
auread.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
371 |
auwrite.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
372 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
373 |
effects/ Subpackage for sound effects |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
374 |
__init__.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
375 |
echo.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
376 |
surround.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
377 |
reverse.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
378 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
379 |
filters/ Subpackage for filters |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
380 |
__init__.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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diff
changeset
|
381 |
equalizer.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
382 |
vocoder.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
383 |
karaoke.py |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
384 |
... |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
385 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
386 |
When importing the package, Python searches through the directories on |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
387 |
``sys.path`` looking for the package subdirectory. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
388 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
389 |
The :file:`__init__.py` files are required to make Python treat the directories |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
390 |
as containing packages; this is done to prevent directories with a common name, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
391 |
such as ``string``, from unintentionally hiding valid modules that occur later |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
392 |
on the module search path. In the simplest case, :file:`__init__.py` can just be |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
393 |
an empty file, but it can also execute initialization code for the package or |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
394 |
set the ``__all__`` variable, described later. |
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
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parents:
diff
changeset
|
396 |
Users of the package can import individual modules from the package, for |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
397 |
example:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
398 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
399 |
import sound.effects.echo |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
400 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
401 |
This loads the submodule :mod:`sound.effects.echo`. It must be referenced with |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
402 |
its full name. :: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
403 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
404 |
sound.effects.echo.echofilter(input, output, delay=0.7, atten=4) |
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 |
An alternative way of importing the submodule is:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
407 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
408 |
from sound.effects import echo |
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 |
This also loads the submodule :mod:`echo`, and makes it available without its |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
411 |
package prefix, so it can be used as follows:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
412 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
413 |
echo.echofilter(input, output, delay=0.7, atten=4) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
414 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
415 |
Yet another variation is to import the desired function or variable directly:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
416 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
417 |
from sound.effects.echo import echofilter |
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 |
Again, this loads the submodule :mod:`echo`, but this makes its function |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
420 |
:func:`echofilter` directly available:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
421 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
422 |
echofilter(input, output, delay=0.7, atten=4) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
423 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
424 |
Note that when using ``from package import item``, the item can be either a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
425 |
submodule (or subpackage) of the package, or some other name defined in the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
426 |
package, like a function, class or variable. The ``import`` statement first |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
427 |
tests whether the item is defined in the package; if not, it assumes it is a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
428 |
module and attempts to load it. If it fails to find it, an :exc:`ImportError` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
429 |
exception is raised. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
430 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
431 |
Contrarily, when using syntax like ``import item.subitem.subsubitem``, each item |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
432 |
except for the last must be a package; the last item can be a module or a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
433 |
package but can't be a class or function or variable defined in the previous |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
434 |
item. |
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 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
437 |
.. _tut-pkg-import-star: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
438 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
439 |
Importing \* From a Package |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
440 |
--------------------------- |
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 |
.. index:: single: __all__ |
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 |
Now what happens when the user writes ``from sound.effects import *``? Ideally, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
445 |
one would hope that this somehow goes out to the filesystem, finds which |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
446 |
submodules are present in the package, and imports them all. Unfortunately, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
447 |
this operation does not work very well on Windows platforms, where the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
448 |
filesystem does not always have accurate information about the case of a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
449 |
filename! On these platforms, there is no guaranteed way to know whether a file |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
450 |
:file:`ECHO.PY` should be imported as a module :mod:`echo`, :mod:`Echo` or |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
451 |
:mod:`ECHO`. (For example, Windows 95 has the annoying practice of showing all |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
452 |
file names with a capitalized first letter.) The DOS 8+3 filename restriction |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
453 |
adds another interesting problem for long module names. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
454 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
455 |
The only solution is for the package author to provide an explicit index of the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
456 |
package. The import statement uses the following convention: if a package's |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
457 |
:file:`__init__.py` code defines a list named ``__all__``, it is taken to be the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
458 |
list of module names that should be imported when ``from package import *`` is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
459 |
encountered. It is up to the package author to keep this list up-to-date when a |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
460 |
new version of the package is released. Package authors may also decide not to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
461 |
support it, if they don't see a use for importing \* from their package. For |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
462 |
example, the file :file:`sounds/effects/__init__.py` could contain the following |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
463 |
code:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
464 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
465 |
__all__ = ["echo", "surround", "reverse"] |
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 |
This would mean that ``from sound.effects import *`` would import the three |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
468 |
named submodules of the :mod:`sound` package. |
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 |
If ``__all__`` is not defined, the statement ``from sound.effects import *`` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
471 |
does *not* import all submodules from the package :mod:`sound.effects` into the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
472 |
current namespace; it only ensures that the package :mod:`sound.effects` has |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
473 |
been imported (possibly running any initialization code in :file:`__init__.py`) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
474 |
and then imports whatever names are defined in the package. This includes any |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
475 |
names defined (and submodules explicitly loaded) by :file:`__init__.py`. It |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
476 |
also includes any submodules of the package that were explicitly loaded by |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
477 |
previous import statements. Consider this code:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
478 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
479 |
import sound.effects.echo |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
480 |
import sound.effects.surround |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
481 |
from sound.effects import * |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
482 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
483 |
In this example, the echo and surround modules are imported in the current |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
484 |
namespace because they are defined in the :mod:`sound.effects` package when the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
485 |
``from...import`` statement is executed. (This also works when ``__all__`` is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
486 |
defined.) |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
487 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
488 |
Note that in general the practice of importing ``*`` from a module or package is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
489 |
frowned upon, since it often causes poorly readable code. However, it is okay to |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
490 |
use it to save typing in interactive sessions, and certain modules are designed |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
491 |
to export only names that follow certain patterns. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
492 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
493 |
Remember, there is nothing wrong with using ``from Package import |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
494 |
specific_submodule``! In fact, this is the recommended notation unless the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
495 |
importing module needs to use submodules with the same name from different |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
496 |
packages. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
497 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
498 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
499 |
Intra-package References |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
500 |
------------------------ |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
501 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
502 |
The submodules often need to refer to each other. For example, the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
503 |
:mod:`surround` module might use the :mod:`echo` module. In fact, such |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
504 |
references are so common that the :keyword:`import` statement first looks in the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
505 |
containing package before looking in the standard module search path. Thus, the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
506 |
:mod:`surround` module can simply use ``import echo`` or ``from echo import |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
507 |
echofilter``. If the imported module is not found in the current package (the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
508 |
package of which the current module is a submodule), the :keyword:`import` |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
509 |
statement looks for a top-level module with the given name. |
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 |
When packages are structured into subpackages (as with the :mod:`sound` package |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
512 |
in the example), you can use absolute imports to refer to submodules of siblings |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
513 |
packages. For example, if the module :mod:`sound.filters.vocoder` needs to use |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
514 |
the :mod:`echo` module in the :mod:`sound.effects` package, it can use ``from |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
515 |
sound.effects import echo``. |
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 |
Starting with Python 2.5, in addition to the implicit relative imports described |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
518 |
above, you can write explicit relative imports with the ``from module import |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
519 |
name`` form of import statement. These explicit relative imports use leading |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
520 |
dots to indicate the current and parent packages involved in the relative |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
521 |
import. From the :mod:`surround` module for example, you might use:: |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
522 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
523 |
from . import echo |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
524 |
from .. import formats |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
525 |
from ..filters import equalizer |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
526 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
527 |
Note that both explicit and implicit relative imports are based on the name of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
528 |
the current module. Since the name of the main module is always ``"__main__"``, |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
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changeset
|
529 |
modules intended for use as the main module of a Python application should |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
530 |
always use absolute imports. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
531 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
532 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
533 |
Packages in Multiple Directories |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
534 |
-------------------------------- |
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 |
Packages support one more special attribute, :attr:`__path__`. This is |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
537 |
initialized to be a list containing the name of the directory holding the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
538 |
package's :file:`__init__.py` before the code in that file is executed. This |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
539 |
variable can be modified; doing so affects future searches for modules and |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
540 |
subpackages contained in the package. |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
541 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
542 |
While this feature is not often needed, it can be used to extend the set of |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
543 |
modules found in a package. |
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 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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changeset
|
546 |
.. rubric:: Footnotes |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
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parents:
diff
changeset
|
547 |
|
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
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changeset
|
548 |
.. [#] In fact function definitions are also 'statements' that are 'executed'; the |
2fb8b9db1c86
Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
549 |
execution enters the function name in the module's global symbol table. |
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Initial QEMU (symbian-qemu-0.9.1-12) import
martin.trojer@nokia.com
parents:
diff
changeset
|
550 |