cpython/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.
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Errors are reported as exceptions; the usual exceptions are given for type
Merged revisions 59921-59932 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59923 | raymond.hettinger | 2008-01-11 19:04:55 +0100 (Fri, 11 Jan 2008) | 1 line Speed-up and simplify code urlparse's result objects. ........ r59924 | andrew.kuchling | 2008-01-11 20:33:24 +0100 (Fri, 11 Jan 2008) | 1 line Bug #1790: update link; remove outdated paragraph ........ r59925 | thomas.heller | 2008-01-11 20:34:06 +0100 (Fri, 11 Jan 2008) | 5 lines Raise an error instead of crashing with a segfault when a NULL function pointer is called. Will backport to release25-maint. ........ r59927 | thomas.heller | 2008-01-11 21:29:19 +0100 (Fri, 11 Jan 2008) | 4 lines Fix a potential 'SystemError: NULL result without error'. NULL may be a valid return value from PyLong_AsVoidPtr. Will backport to release25-maint. ........ r59928 | raymond.hettinger | 2008-01-12 00:25:18 +0100 (Sat, 12 Jan 2008) | 1 line Update the opcode docs for STORE_MAP and BUILD_MAP ........ r59929 | mark.dickinson | 2008-01-12 02:56:00 +0100 (Sat, 12 Jan 2008) | 4 lines Issue 1780: Allow leading and trailing whitespace in Decimal constructor, when constructing from a string. Disallow trailing newlines in Context.create_decimal. ........ r59930 | georg.brandl | 2008-01-12 11:53:29 +0100 (Sat, 12 Jan 2008) | 3 lines Move OSError docs to exceptions doc, remove obsolete descriptions from os docs, rework posix docs. ........ r59931 | georg.brandl | 2008-01-12 14:47:57 +0100 (Sat, 12 Jan 2008) | 3 lines Patch #1700288: Method cache optimization, by Armin Rigo, ported to 2.6 by Kevin Jacobs. ........ r59932 | georg.brandl | 2008-01-12 17:11:09 +0100 (Sat, 12 Jan 2008) | 2 lines Fix editing glitch. ........
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errors, while errors reported by the system calls raise :exc:`OSError`.
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.. _posix-large-files:
Large File Support
------------------
.. index::
single: large files
single: file; large files
.. sectionauthor:: Steve Clift <clift@mail.anacapa.net>
Merged revisions 59921-59932 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59923 | raymond.hettinger | 2008-01-11 19:04:55 +0100 (Fri, 11 Jan 2008) | 1 line Speed-up and simplify code urlparse's result objects. ........ r59924 | andrew.kuchling | 2008-01-11 20:33:24 +0100 (Fri, 11 Jan 2008) | 1 line Bug #1790: update link; remove outdated paragraph ........ r59925 | thomas.heller | 2008-01-11 20:34:06 +0100 (Fri, 11 Jan 2008) | 5 lines Raise an error instead of crashing with a segfault when a NULL function pointer is called. Will backport to release25-maint. ........ r59927 | thomas.heller | 2008-01-11 21:29:19 +0100 (Fri, 11 Jan 2008) | 4 lines Fix a potential 'SystemError: NULL result without error'. NULL may be a valid return value from PyLong_AsVoidPtr. Will backport to release25-maint. ........ r59928 | raymond.hettinger | 2008-01-12 00:25:18 +0100 (Sat, 12 Jan 2008) | 1 line Update the opcode docs for STORE_MAP and BUILD_MAP ........ r59929 | mark.dickinson | 2008-01-12 02:56:00 +0100 (Sat, 12 Jan 2008) | 4 lines Issue 1780: Allow leading and trailing whitespace in Decimal constructor, when constructing from a string. Disallow trailing newlines in Context.create_decimal. ........ r59930 | georg.brandl | 2008-01-12 11:53:29 +0100 (Sat, 12 Jan 2008) | 3 lines Move OSError docs to exceptions doc, remove obsolete descriptions from os docs, rework posix docs. ........ r59931 | georg.brandl | 2008-01-12 14:47:57 +0100 (Sat, 12 Jan 2008) | 3 lines Patch #1700288: Method cache optimization, by Armin Rigo, ported to 2.6 by Kevin Jacobs. ........ r59932 | georg.brandl | 2008-01-12 17:11:09 +0100 (Sat, 12 Jan 2008) | 2 lines Fix editing glitch. ........
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Several operating systems (including AIX, HP-UX, Irix and Solaris) provide
support for files that are larger than 2 GiB from a C programming model where
:c:type:`int` and :c:type:`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
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`.
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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::
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CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
./configure
.. _posix-contents:
Merged revisions 59921-59932 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59923 | raymond.hettinger | 2008-01-11 19:04:55 +0100 (Fri, 11 Jan 2008) | 1 line Speed-up and simplify code urlparse's result objects. ........ r59924 | andrew.kuchling | 2008-01-11 20:33:24 +0100 (Fri, 11 Jan 2008) | 1 line Bug #1790: update link; remove outdated paragraph ........ r59925 | thomas.heller | 2008-01-11 20:34:06 +0100 (Fri, 11 Jan 2008) | 5 lines Raise an error instead of crashing with a segfault when a NULL function pointer is called. Will backport to release25-maint. ........ r59927 | thomas.heller | 2008-01-11 21:29:19 +0100 (Fri, 11 Jan 2008) | 4 lines Fix a potential 'SystemError: NULL result without error'. NULL may be a valid return value from PyLong_AsVoidPtr. Will backport to release25-maint. ........ r59928 | raymond.hettinger | 2008-01-12 00:25:18 +0100 (Sat, 12 Jan 2008) | 1 line Update the opcode docs for STORE_MAP and BUILD_MAP ........ r59929 | mark.dickinson | 2008-01-12 02:56:00 +0100 (Sat, 12 Jan 2008) | 4 lines Issue 1780: Allow leading and trailing whitespace in Decimal constructor, when constructing from a string. Disallow trailing newlines in Context.create_decimal. ........ r59930 | georg.brandl | 2008-01-12 11:53:29 +0100 (Sat, 12 Jan 2008) | 3 lines Move OSError docs to exceptions doc, remove obsolete descriptions from os docs, rework posix docs. ........ r59931 | georg.brandl | 2008-01-12 14:47:57 +0100 (Sat, 12 Jan 2008) | 3 lines Patch #1700288: Method cache optimization, by Armin Rigo, ported to 2.6 by Kevin Jacobs. ........ r59932 | georg.brandl | 2008-01-12 17:11:09 +0100 (Sat, 12 Jan 2008) | 2 lines Fix editing glitch. ........
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Notable Module Contents
-----------------------
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Merged revisions 59921-59932 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59923 | raymond.hettinger | 2008-01-11 19:04:55 +0100 (Fri, 11 Jan 2008) | 1 line Speed-up and simplify code urlparse's result objects. ........ r59924 | andrew.kuchling | 2008-01-11 20:33:24 +0100 (Fri, 11 Jan 2008) | 1 line Bug #1790: update link; remove outdated paragraph ........ r59925 | thomas.heller | 2008-01-11 20:34:06 +0100 (Fri, 11 Jan 2008) | 5 lines Raise an error instead of crashing with a segfault when a NULL function pointer is called. Will backport to release25-maint. ........ r59927 | thomas.heller | 2008-01-11 21:29:19 +0100 (Fri, 11 Jan 2008) | 4 lines Fix a potential 'SystemError: NULL result without error'. NULL may be a valid return value from PyLong_AsVoidPtr. Will backport to release25-maint. ........ r59928 | raymond.hettinger | 2008-01-12 00:25:18 +0100 (Sat, 12 Jan 2008) | 1 line Update the opcode docs for STORE_MAP and BUILD_MAP ........ r59929 | mark.dickinson | 2008-01-12 02:56:00 +0100 (Sat, 12 Jan 2008) | 4 lines Issue 1780: Allow leading and trailing whitespace in Decimal constructor, when constructing from a string. Disallow trailing newlines in Context.create_decimal. ........ r59930 | georg.brandl | 2008-01-12 11:53:29 +0100 (Sat, 12 Jan 2008) | 3 lines Move OSError docs to exceptions doc, remove obsolete descriptions from os docs, rework posix docs. ........ r59931 | georg.brandl | 2008-01-12 14:47:57 +0100 (Sat, 12 Jan 2008) | 3 lines Patch #1700288: Method cache optimization, by Armin Rigo, ported to 2.6 by Kevin Jacobs. ........ r59932 | georg.brandl | 2008-01-12 17:11:09 +0100 (Sat, 12 Jan 2008) | 2 lines Fix editing glitch. ........
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In addition to many functions described in the :mod:`os` module documentation,
:mod:`posix` defines the following data item:
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.. data:: environ
Merged revisions 59921-59932 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r59923 | raymond.hettinger | 2008-01-11 19:04:55 +0100 (Fri, 11 Jan 2008) | 1 line Speed-up and simplify code urlparse's result objects. ........ r59924 | andrew.kuchling | 2008-01-11 20:33:24 +0100 (Fri, 11 Jan 2008) | 1 line Bug #1790: update link; remove outdated paragraph ........ r59925 | thomas.heller | 2008-01-11 20:34:06 +0100 (Fri, 11 Jan 2008) | 5 lines Raise an error instead of crashing with a segfault when a NULL function pointer is called. Will backport to release25-maint. ........ r59927 | thomas.heller | 2008-01-11 21:29:19 +0100 (Fri, 11 Jan 2008) | 4 lines Fix a potential 'SystemError: NULL result without error'. NULL may be a valid return value from PyLong_AsVoidPtr. Will backport to release25-maint. ........ r59928 | raymond.hettinger | 2008-01-12 00:25:18 +0100 (Sat, 12 Jan 2008) | 1 line Update the opcode docs for STORE_MAP and BUILD_MAP ........ r59929 | mark.dickinson | 2008-01-12 02:56:00 +0100 (Sat, 12 Jan 2008) | 4 lines Issue 1780: Allow leading and trailing whitespace in Decimal constructor, when constructing from a string. Disallow trailing newlines in Context.create_decimal. ........ r59930 | georg.brandl | 2008-01-12 11:53:29 +0100 (Sat, 12 Jan 2008) | 3 lines Move OSError docs to exceptions doc, remove obsolete descriptions from os docs, rework posix docs. ........ r59931 | georg.brandl | 2008-01-12 14:47:57 +0100 (Sat, 12 Jan 2008) | 3 lines Patch #1700288: Method cache optimization, by Armin Rigo, ported to 2.6 by Kevin Jacobs. ........ r59932 | georg.brandl | 2008-01-12 17:11:09 +0100 (Sat, 12 Jan 2008) | 2 lines Fix editing glitch. ........
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A dictionary representing the string environment at the time the interpreter
was started. Keys and values are bytes on Unix and str on Windows. For
example, ``environ[b'HOME']`` (``environ['HOME']`` on Windows) is the
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
: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`.
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.. versionchanged:: 3.2
On Unix, keys and values are bytes.
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.. note::
The :mod:`os` module provides an alternate implementation of ``environ``
which updates the environment on modification. Note also that updating
:data:`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.