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python/vendor/Python-2.7.6/Doc/library/posix.rst
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:mod:`posix` --- The most common POSIX system calls
.. module:: posix :platform: Unix :synopsis: The most common POSIX system calls (normally used via module os).
This module provides access to operating system functionality that is standardized by the C Standard and the POSIX standard (a thinly disguised Unix interface).
.. index:: module: os
Do not import this module directly. Instead, import the module :mod:`os`, which provides a portable version of this interface. On Unix, the :mod:`os` module provides a superset of the :mod:`posix` interface. On non-Unix operating systems the :mod:`posix` module is not available, but a subset is always available through the :mod:`os` interface. Once :mod:`os` is imported, there is no performance penalty in using it instead of :mod:`posix`. In addition, :mod:`os` provides some additional functionality, such as automatically calling :func:`~os.putenv` when an entry in os.environ is changed.
Errors are reported as exceptions; the usual exceptions are given for type errors, while errors reported by the system calls raise :exc:`OSError`.
Large File Support
.. index:: single: large files single: file; large files
.. sectionauthor:: Steve Clift <clift@mail.anacapa.net>
Several operating systems (including AIX, HP-UX, Irix and Solaris) provide support for files that are larger than 2 GB from a C programming model where :c:type:`int` and :c:type:`long` are 32-bit values. This is typically accomplished by defining the relevant size and offset types as 64-bit values. Such files are sometimes referred to as :dfn:`large files`.
Large file support is enabled in Python when the size of an :c:type:`off_t` is larger than a :c:type:`long` and the :c:type:`long long` type is available and is at least as large as an :c:type:`off_t`. Python longs are then used to represent file sizes, offsets and other values that can exceed the range of a Python int. It may be necessary to configure and compile Python with certain compiler flags to enable this mode. For example, it is enabled by default with recent versions of Irix, but with Solaris 2.6 and 2.7 you need to do something like:
CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
./configure
On large-file-capable Linux systems, this might work:
CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
./configure
Notable Module Contents
In addition to many functions described in the :mod:`os` module documentation, :mod:`posix` defines the following data item:
.. data:: environ
A dictionary representing the string environment at the time the interpreter
was started. For example, ``environ['HOME']`` is the pathname of your home
directory, equivalent to ``getenv("HOME")`` in C.
Modifying this dictionary does not affect the string environment passed on by
:func:`~os.execv`, :func:`~os.popen` or :func:`~os.system`; if you need to
change the environment, pass ``environ`` to :func:`~os.execve` or add
variable assignments and export statements to the command string for
:func:`~os.system` or :func:`~os.popen`.
.. note::
The :mod:`os` module provides an alternate implementation of ``environ`` which
updates the environment on modification. Note also that updating ``os.environ``
will render this dictionary obsolete. Use of the :mod:`os` module version of
this is recommended over direct access to the :mod:`posix` module.
