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1 :mod:`posix` --- The most common POSIX system calls |
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2 =================================================== |
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3 |
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4 .. module:: posix |
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5 :platform: Unix |
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6 :synopsis: The most common POSIX system calls (normally used via module os). |
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7 |
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8 |
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9 This module provides access to operating system functionality that is |
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10 standardized by the C Standard and the POSIX standard (a thinly disguised Unix |
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11 interface). |
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12 |
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13 .. index:: module: os |
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14 |
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15 **Do not import this module directly.** Instead, import the module :mod:`os`, |
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16 which provides a *portable* version of this interface. On Unix, the :mod:`os` |
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17 module provides a superset of the :mod:`posix` interface. On non-Unix operating |
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18 systems the :mod:`posix` module is not available, but a subset is always |
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19 available through the :mod:`os` interface. Once :mod:`os` is imported, there is |
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20 *no* performance penalty in using it instead of :mod:`posix`. In addition, |
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21 :mod:`os` provides some additional functionality, such as automatically calling |
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22 :func:`putenv` when an entry in ``os.environ`` is changed. |
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23 |
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24 Errors are reported as exceptions; the usual exceptions are given for type |
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25 errors, while errors reported by the system calls raise :exc:`OSError`. |
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26 |
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27 |
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28 .. _posix-large-files: |
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29 |
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30 Large File Support |
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31 ------------------ |
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32 |
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33 .. index:: |
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34 single: large files |
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35 single: file; large files |
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36 |
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37 .. sectionauthor:: Steve Clift <clift@mail.anacapa.net> |
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38 |
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39 Several operating systems (including AIX, HP-UX, Irix and Solaris) provide |
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40 support for files that are larger than 2 GB from a C programming model where |
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41 :ctype:`int` and :ctype:`long` are 32-bit values. This is typically accomplished |
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42 by defining the relevant size and offset types as 64-bit values. Such files are |
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43 sometimes referred to as :dfn:`large files`. |
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44 |
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45 Large file support is enabled in Python when the size of an :ctype:`off_t` is |
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46 larger than a :ctype:`long` and the :ctype:`long long` type is available and is |
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47 at least as large as an :ctype:`off_t`. Python longs are then used to represent |
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48 file sizes, offsets and other values that can exceed the range of a Python int. |
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49 It may be necessary to configure and compile Python with certain compiler flags |
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50 to enable this mode. For example, it is enabled by default with recent versions |
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51 of Irix, but with Solaris 2.6 and 2.7 you need to do something like:: |
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52 |
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53 CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \ |
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54 ./configure |
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55 |
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56 On large-file-capable Linux systems, this might work:: |
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57 |
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58 CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \ |
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59 ./configure |
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60 |
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61 |
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62 .. _posix-contents: |
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63 |
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64 Notable Module Contents |
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65 ----------------------- |
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66 |
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67 In addition to many functions described in the :mod:`os` module documentation, |
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68 :mod:`posix` defines the following data item: |
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69 |
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70 .. data:: environ |
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71 |
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72 A dictionary representing the string environment at the time the interpreter |
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73 was started. For example, ``environ['HOME']`` is the pathname of your home |
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74 directory, equivalent to ``getenv("HOME")`` in C. |
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75 |
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76 Modifying this dictionary does not affect the string environment passed on by |
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77 :func:`execv`, :func:`popen` or :func:`system`; if you need to change the |
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78 environment, pass ``environ`` to :func:`execve` or add variable assignments and |
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79 export statements to the command string for :func:`system` or :func:`popen`. |
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80 |
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81 .. note:: |
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82 |
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83 The :mod:`os` module provides an alternate implementation of ``environ`` which |
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84 updates the environment on modification. Note also that updating ``os.environ`` |
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85 will render this dictionary obsolete. Use of the :mod:`os` module version of |
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86 this is recommended over direct access to the :mod:`posix` module. |