/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:`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`.
- .. _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, HP-UX, 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::
- CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
- ./configure
- .. _posix-contents:
- 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:`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.