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 10 This module provides access to operating system functionality that is 11 standardized by the C Standard and the POSIX standard (a thinly disguised Unix 12 interface). 13 14 .. index:: module: os 15 16 **Do not import this module directly.** Instead, import the module :mod:`os`, 17 which provides a *portable* version of this interface. On Unix, the :mod:`os` 18 module provides a superset of the :mod:`posix` interface. On non-Unix operating 19 systems the :mod:`posix` module is not available, but a subset is always 20 available 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 25 Errors are reported as exceptions; the usual exceptions are given for type 26 errors, while errors reported by the system calls raise :exc:`OSError`. 27 28 29 .. _posix-large-files: 30 31 Large File Support 32 ------------------ 33 34 .. index:: 35 single: large files 36 single: file; large files 37 38 .. sectionauthor:: Steve Clift <clift (a] mail.anacapa.net> 39 40 Several operating systems (including AIX, HP-UX, Irix and Solaris) provide 41 support 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 43 by defining the relevant size and offset types as 64-bit values. Such files are 44 sometimes referred to as :dfn:`large files`. 45 46 Large file support is enabled in Python when the size of an :c:type:`off_t` is 47 larger than a :c:type:`long` and the :c:type:`long long` type is available and is 48 at least as large as an :c:type:`off_t`. 49 It may be necessary to configure and compile Python with certain compiler flags 50 to enable this mode. For example, it is enabled by default with recent versions 51 of Irix, but with Solaris 2.6 and 2.7 you need to do something like:: 52 53 CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \ 54 ./configure 55 56 On 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 64 Notable Module Contents 65 ----------------------- 66 67 In 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
