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