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authorGeorg Brandl <georg@python.org>2007-08-15 14:28:22 (GMT)
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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:`putenv` when an entry in ``os.environ`` is changed.
+
+The descriptions below are very terse; refer to the corresponding Unix manual
+(or POSIX documentation) entry for more information. Arguments called *path*
+refer to a pathname given as a string.
+
+Errors are reported as exceptions; the usual exceptions are given for type
+errors, while errors reported by the system calls raise :exc:`error` (a synonym
+for the standard exception :exc:`OSError`), described below.
+
+
+.. _posix-large-files:
+
+Large File Support
+------------------
+
+.. index::
+ single: large files
+ single: file; large files
+
+.. sectionauthor:: Steve Clift <clift@mail.anacapa.net>
+
+
+Several operating systems (including AIX, HPUX, Irix and Solaris) provide
+support for files that are larger than 2 Gb from a C programming model where
+:ctype:`int` and :ctype:`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 :ctype:`off_t` is
+larger than a :ctype:`long` and the :ctype:`long long` type is available and is
+at least as large as an :ctype:`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:
+
+.. % $ <-- bow to font-lock
+
+::
+
+ CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
+ ./configure
+
+.. % $ <-- bow to font-lock
+
+
+.. _posix-contents:
+
+Module Contents
+---------------
+
+Module :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:`execv`, :func:`popen` or :func:`system`; if you need to change the
+ environment, pass ``environ`` to :func:`execve` or add variable assignments and
+ export statements to the command string for :func:`system` or :func:`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.
+
+Additional contents of this module should only be accessed via the :mod:`os`
+module; refer to the documentation for that module for further information.
+