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99 lines
4.0 KiB
TeX
99 lines
4.0 KiB
TeX
\section{\module{posix} ---
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The most common \POSIX{} system calls}
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\declaremodule{builtin}{posix}
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\platform{Unix}
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\modulesynopsis{The most common \POSIX{} system calls (normally used
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via module \refmodule{os}).}
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This module provides access to operating system functionality that is
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standardized by the C Standard and the \POSIX{} standard (a thinly
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disguised \UNIX{} interface).
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\strong{Do not import this module directly.} Instead, import the
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module \refmodule{os}, which provides a \emph{portable} version of this
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interface. On \UNIX{}, the \refmodule{os} module provides a superset of
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the \module{posix} interface. On non-\UNIX{} operating systems the
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\module{posix} module is not available, but a subset is always
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available through the \refmodule{os} interface. Once \refmodule{os} is
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imported, there is \emph{no} performance penalty in using it instead
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of \module{posix}. In addition, \refmodule{os}\refstmodindex{os}
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provides some additional functionality, such as automatically calling
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\function{putenv()} when an entry in \code{os.environ} is changed.
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The descriptions below are very terse; refer to the corresponding
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\UNIX{} manual (or \POSIX{} documentation) entry for more information.
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Arguments called \var{path} refer to a pathname given as a string.
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Errors are reported as exceptions; the usual exceptions are given for
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type errors, while errors reported by the system calls raise
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\exception{error} (a synonym for the standard exception
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\exception{OSError}), described below.
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\subsection{Large File Support \label{posix-large-files}}
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\sectionauthor{Steve Clift}{clift@mail.anacapa.net}
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\index{large files}
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\index{file!large files}
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Several operating systems (including AIX, HPUX, Irix and Solaris)
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provide support for files that are larger than 2 Gb from a C
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programming model where \ctype{int} and \ctype{long} are 32-bit
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values. This is typically accomplished by defining the relevant size
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and offset types as 64-bit values. Such files are sometimes referred
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to as \dfn{large files}.
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Large file support is enabled in Python when the size of an
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\ctype{off_t} is larger than a \ctype{long} and the \ctype{long long}
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type is available and is at least as large as an \ctype{off_t}. Python
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longs are then used to represent file sizes, offsets and other values
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that can exceed the range of a Python int. It may be necessary to
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configure and compile Python with certain compiler flags to enable
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this mode. For example, it is enabled by default with recent versions
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of Irix, but with Solaris 2.6 and 2.7 you need to do something like:
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\begin{verbatim}
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CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
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./configure
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\end{verbatim} % $ <-- bow to font-lock
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On large-file-capable Linux systems, this might work:
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\begin{verbatim}
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CC="-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64"
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export CC
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./configure
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\end{verbatim}
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\subsection{Module Contents \label{posix-contents}}
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Module \module{posix} defines the following data item:
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\begin{datadesc}{environ}
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A dictionary representing the string environment at the time the
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interpreter was started. For example, \code{environ['HOME']} is the
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pathname of your home directory, equivalent to
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\code{getenv("HOME")} in C.
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Modifying this dictionary does not affect the string environment
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passed on by \function{execv()}, \function{popen()} or
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\function{system()}; if you need to change the environment, pass
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\code{environ} to \function{execve()} or add variable assignments and
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export statements to the command string for \function{system()} or
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\function{popen()}.
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\strong{Note:} The \refmodule{os} module provides an alternate
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implementation of \code{environ} which updates the environment on
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modification. Note also that updating \code{os.environ} will render
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this dictionary obsolete. Use of the \refmodule{os} for this is
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recommended over direct access to the \module{posix} module.
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\end{datadesc}
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Additional contents of this module should only be accessed via the
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\refmodule{os} module; refer to the documentation for that module for
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further information.
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