1:mod:`posix` --- The most common POSIX system calls 2=================================================== 3 4.. module:: posix 5 :platform: Unix 6 :synopsis: The most common POSIX system calls (normally used via module os). 7 8-------------- 9 10This module provides access to operating system functionality that is 11standardized by the C Standard and the POSIX standard (a thinly disguised Unix 12interface). 13 14.. index:: module: os 15 16**Do not import this module directly.** Instead, import the module :mod:`os`, 17which provides a *portable* version of this interface. On Unix, the :mod:`os` 18module provides a superset of the :mod:`posix` interface. On non-Unix operating 19systems the :mod:`posix` module is not available, but a subset is always 20available through the :mod:`os` interface. Once :mod:`os` is imported, there is 21*no* performance penalty in using it instead of :mod:`posix`. In addition, 22:mod:`os` provides some additional functionality, such as automatically calling 23:func:`~os.putenv` when an entry in ``os.environ`` is changed. 24 25Errors are reported as exceptions; the usual exceptions are given for type 26errors, while errors reported by the system calls raise :exc:`OSError`. 27 28 29.. _posix-large-files: 30 31Large File Support 32------------------ 33 34.. index:: 35 single: large files 36 single: file; large files 37 38.. sectionauthor:: Steve Clift <clift@mail.anacapa.net> 39 40Several operating systems (including AIX, HP-UX and Solaris) provide 41support for files that are larger than 2 GiB from a C programming model where 42:c:type:`int` and :c:type:`long` are 32-bit values. This is typically accomplished 43by defining the relevant size and offset types as 64-bit values. Such files are 44sometimes referred to as :dfn:`large files`. 45 46Large file support is enabled in Python when the size of an :c:type:`off_t` is 47larger than a :c:type:`long` and the :c:type:`long long` is at least as large 48as an :c:type:`off_t`. 49It may be necessary to configure and compile Python with certain compiler flags 50to enable this mode. For example, with Solaris 2.6 and 2.7 you need to do 51something like:: 52 53 CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \ 54 ./configure 55 56On large-file-capable Linux systems, this might work:: 57 58 CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \ 59 ./configure 60 61 62.. _posix-contents: 63 64Notable Module Contents 65----------------------- 66 67In addition to many functions described in the :mod:`os` module documentation, 68:mod:`posix` defines the following data item: 69 70.. data:: environ 71 72 A dictionary representing the string environment at the time the interpreter 73 was started. Keys and values are bytes on Unix and str on Windows. For 74 example, ``environ[b'HOME']`` (``environ['HOME']`` on Windows) is the 75 pathname of your home directory, equivalent to ``getenv("HOME")`` in C. 76 77 Modifying this dictionary does not affect the string environment passed on by 78 :func:`~os.execv`, :func:`~os.popen` or :func:`~os.system`; if you need to 79 change the environment, pass ``environ`` to :func:`~os.execve` or add 80 variable assignments and export statements to the command string for 81 :func:`~os.system` or :func:`~os.popen`. 82 83 .. versionchanged:: 3.2 84 On Unix, keys and values are bytes. 85 86 .. note:: 87 88 The :mod:`os` module provides an alternate implementation of ``environ`` 89 which updates the environment on modification. Note also that updating 90 :data:`os.environ` will render this dictionary obsolete. Use of the 91 :mod:`os` module version of this is recommended over direct access to the 92 :mod:`posix` module. 93