posix —- The most common POSIX system calls

This module provides access to operating system functionality that isstandardized by the C Standard and the POSIX standard (a thinly disguised Unixinterface).

Do not import this module directly. Instead, import the module os,which provides a portable version of this interface. On Unix, the osmodule provides a superset of the posix interface. On non-Unix operatingsystems the posix module is not available, but a subset is alwaysavailable through the os interface. Once os is imported, there isno performance penalty in using it instead of posix. In addition,os provides some additional functionality, such as automatically callingputenv() when an entry in os.environ is changed.

Errors are reported as exceptions; the usual exceptions are given for typeerrors, while errors reported by the system calls raise OSError.

Large File Support

Several operating systems (including AIX, HP-UX, Irix and Solaris) providesupport for files that are larger than 2 GiB from a C programming model whereint and long are 32-bit values. This is typically accomplishedby defining the relevant size and offset types as 64-bit values. Such files aresometimes referred to as large files.

Large file support is enabled in Python when the size of an off_t islarger than a long and the long long is at least as largeas an off_t.It may be necessary to configure and compile Python with certain compiler flagsto enable this mode. For example, it is enabled by default with recent versionsof Irix, but with Solaris 2.6 and 2.7 you need to do something like:

  1. CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
  2.         ./configure

On large-file-capable Linux systems, this might work:

  1. CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
  2.         ./configure

Notable Module Contents

In addition to many functions described in the os module documentation,posix defines the following data item:

  • posix.environ
  • A dictionary representing the string environment at the time the interpreterwas started. Keys and values are bytes on Unix and str on Windows. Forexample, environ[b'HOME'] (environ['HOME'] on Windows) is thepathname of your home directory, equivalent to getenv("HOME") in C.

Modifying this dictionary does not affect the string environment passed on byexecv(), popen() or system(); if you need tochange the environment, pass environ to execve() or addvariable assignments and export statements to the command string forsystem() or popen().

在 3.2 版更改: On Unix, keys and values are bytes.

注解

The os module provides an alternate implementation of environwhich updates the environment on modification. Note also that updatingos.environ will render this dictionary obsolete. Use of theos module version of this is recommended over direct access to theposix module.