| \section{\module{posix} --- |
| The most common \POSIX{} system calls} |
| |
| \declaremodule{builtin}{posix} |
| \platform{Unix} |
| \modulesynopsis{The most common \POSIX{} system calls (normally used |
| via module \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). |
| |
| \strong{Do not import this module directly.} Instead, import the |
| module \refmodule{os}, which provides a \emph{portable} version of this |
| interface. On \UNIX{}, the \module{os} module provides a superset of |
| the \module{posix} interface. On non-\UNIX{} operating systems the |
| \module{posix} module is not available, but a subset is always |
| available through the \module{os} interface. Once \module{os} is |
| imported, there is \emph{no} performance penalty in using it instead |
| of \module{posix}. In addition, \module{os}\refstmodindex{os} |
| provides some additional functionality, such as automatically calling |
| \function{putenv()} when an entry in \code{os.environ} is changed. |
| |
| The descriptions below are very terse; refer to the corresponding |
| \UNIX{} manual (or \POSIX{} documentation) entry for more information. |
| Arguments called \var{path} refer to a pathname given as a string. |
| |
| Errors are reported as exceptions; the usual exceptions are given for |
| type errors, while errors reported by the system calls raise |
| \exception{error} (a synonym for the standard exception |
| \exception{OSError}), described below. |
| |
| |
| \subsection{Large File Support \label{posix-large-files}} |
| \sectionauthor{Steve Clift}{clift@mail.anacapa.net} |
| \index{large files} |
| \index{file!large files} |
| |
| |
| Several operating systems (including AIX, HPUX, Irix and Solaris) |
| provide support for files that are larger than 2 Gb from a C |
| programming model where \ctype{int} and \ctype{long} are 32-bit |
| values. This is typically accomplished 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 |
| \ctype{off_t} is larger than a \ctype{long} and the \ctype{long long} |
| type is available and is at least as large as an \ctype{off_t}. Python |
| longs are then used to represent file sizes, offsets and other values |
| that can exceed the range of a Python int. 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: |
| |
| \begin{verbatim} |
| CFLAGS="-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64" OPT="-g -O2 $CFLAGS" \ |
| configure |
| \end{verbatim} % $ <-- bow to font-lock |
| |
| |
| \subsection{Module Contents \label{posix-contents}} |
| |
| |
| Module \module{posix} defines the following data item: |
| |
| \begin{datadesc}{environ} |
| A dictionary representing the string environment at the time the |
| interpreter was started. For example, \code{environ['HOME']} is the |
| pathname of your home directory, equivalent to \code{getenv("HOME")} |
| in C. |
| |
| Modifying this dictionary does not affect the string environment |
| passed on by \function{execv()}, \function{popen()} or |
| \function{system()}; if you need to change the environment, pass |
| \code{environ} to \function{execve()} or add variable assignments and |
| export statements to the command string for \function{system()} or |
| \function{popen()}. |
| |
| \strong{Note:} The \refmodule{os} module provides an alternate |
| implementation of \code{environ} which updates the environment on |
| modification. Note also that updating \code{os.environ} will render |
| this dictionary obsolete. Use of the \refmodule{os} for this is |
| recommended over direct access to the \module{posix} module. |
| \end{datadesc} |
| |
| Additional contents of this module should only be accessed via the |
| \refmodule{os} module; refer to the documentation for that module for |
| further information. |