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 This module provides access to operating system functionality that is 10 standardized by the C Standard and the POSIX standard (a thinly disguised Unix 11 interface). 12 13 .. index:: module: os 14 15 **Do not import this module directly.** Instead, import the module :mod:`os`, 16 which provides a *portable* version of this interface. On Unix, the :mod:`os` 17 module provides a superset of the :mod:`posix` interface. On non-Unix operating 18 systems the :mod:`posix` module is not available, but a subset is always 19 available through the :mod:`os` interface. Once :mod:`os` is imported, there is 20 *no* performance penalty in using it instead of :mod:`posix`. In addition, 21 :mod:`os` provides some additional functionality, such as automatically calling 22 :func:`~os.putenv` when an entry in ``os.environ`` is changed. 23 24 Errors are reported as exceptions; the usual exceptions are given for type 25 errors, while errors reported by the system calls raise :exc:`OSError`. 26 27 28 .. _posix-large-files: 29 30 Large File Support 31 ------------------ 32 33 .. index:: 34 single: large files 35 single: file; large files 36 37 .. sectionauthor:: Steve Clift <clift (a] mail.anacapa.net> 38 39 Several operating systems (including AIX, HP-UX, Irix and Solaris) provide 40 support for files that are larger than 2 GB from a C programming model where 41 :c:type:`int` and :c:type:`long` are 32-bit values. This is typically accomplished 42 by defining the relevant size and offset types as 64-bit values. Such files are 43 sometimes referred to as :dfn:`large files`. 44 45 Large file support is enabled in Python when the size of an :c:type:`off_t` is 46 larger than a :c:type:`long` and the :c:type:`long long` type is available and is 47 at least as large as an :c:type:`off_t`. Python longs are then used to represent 48 file sizes, offsets and other values that can exceed the range of a Python int. 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. For example, ``environ['HOME']`` is the pathname of your home 74 directory, equivalent to ``getenv("HOME")`` in C. 75 76 Modifying this dictionary does not affect the string environment passed on by 77 :func:`~os.execv`, :func:`~os.popen` or :func:`~os.system`; if you need to 78 change the environment, pass ``environ`` to :func:`~os.execve` or add 79 variable assignments and export statements to the command string for 80 :func:`~os.system` or :func:`~os.popen`. 81 82 .. note:: 83 84 The :mod:`os` module provides an alternate implementation of ``environ`` which 85 updates the environment on modification. Note also that updating ``os.environ`` 86 will render this dictionary obsolete. Use of the :mod:`os` module version of 87 this is recommended over direct access to the :mod:`posix` module. 88
