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94 lines
3.5 KiB
ReStructuredText
94 lines
3.5 KiB
ReStructuredText
:mod:`!posix` --- The most common POSIX system calls
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====================================================
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.. module:: posix
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:platform: Unix
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:synopsis: The most common POSIX system calls (normally used via module os).
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--------------
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This module provides access to operating system functionality that is
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standardized by the C Standard and the POSIX standard (a thinly disguised Unix
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interface).
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.. availability:: Unix.
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.. index:: pair: module; os
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**Do not import this module directly.** Instead, import the module :mod:`os`,
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which provides a *portable* version of this interface. On Unix, the :mod:`os`
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module provides a superset of the :mod:`posix` interface. On non-Unix operating
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systems the :mod:`posix` module is not available, but a subset is always
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available through the :mod:`os` interface. Once :mod:`os` is imported, there is
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*no* performance penalty in using it instead of :mod:`posix`. In addition,
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:mod:`os` provides some additional functionality, such as automatically calling
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:func:`~os.putenv` when an entry in ``os.environ`` is changed.
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Errors are reported as exceptions; the usual exceptions are given for type
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errors, while errors reported by the system calls raise :exc:`OSError`.
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.. _posix-large-files:
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Large File Support
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------------------
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.. index::
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single: large files
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single: file; large files
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.. sectionauthor:: Steve Clift <clift@mail.anacapa.net>
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Several operating systems (including AIX and Solaris) provide
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support for files that are larger than 2 GiB from a C programming model where
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:c:expr:`int` and :c:expr:`long` are 32-bit values. This is typically accomplished
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by defining the relevant size and offset types as 64-bit values. Such files are
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sometimes referred to as :dfn:`large files`.
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Large file support is enabled in Python when the size of an :c:type:`off_t` is
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larger than a :c:expr:`long` and the :c:expr:`long long` is at least as large
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as an :c:type:`off_t`.
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It may be necessary to configure and compile Python with certain compiler flags
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to enable this mode. For example, with Solaris 2.6 and 2.7 you need to do
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something like::
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CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
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./configure
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On large-file-capable Linux systems, this might work::
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CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
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./configure
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.. _posix-contents:
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Notable Module Contents
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-----------------------
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In addition to many functions described in the :mod:`os` module documentation,
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:mod:`posix` defines the following data item:
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.. data:: environ
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A dictionary representing the string environment at the time the interpreter
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was started. Keys and values are bytes on Unix and str on Windows. For
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example, ``environ[b'HOME']`` (``environ['HOME']`` on Windows) is the
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pathname of your home directory, equivalent to ``getenv("HOME")`` in C.
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Modifying this dictionary does not affect the string environment passed on by
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:func:`~os.execv`, :func:`~os.popen` or :func:`~os.system`; if you need to
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change the environment, pass ``environ`` to :func:`~os.execve` or add
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variable assignments and export statements to the command string for
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:func:`~os.system` or :func:`~os.popen`.
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.. versionchanged:: 3.2
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On Unix, keys and values are bytes.
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.. note::
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The :mod:`os` module provides an alternate implementation of ``environ``
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which updates the environment on modification. Note also that updating
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:data:`os.environ` will render this dictionary obsolete. Use of the
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:mod:`os` module version of this is recommended over direct access to the
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:mod:`posix` module.
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