mirror of https://github.com/python/cpython.git
55 lines
2.4 KiB
TeX
55 lines
2.4 KiB
TeX
\section{\module{select} ---
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Waiting for I/O completion}
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\declaremodule{builtin}{select}
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\modulesynopsis{Wait for I/O completion on multiple streams.}
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This module provides access to the function \cfunction{select()}
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available in most operating systems. Note that on Windows, it only
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works for sockets; on other operating systems, it also works for other
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file types (in particular, on \UNIX{}, it works on pipes). It cannot
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be used or regular files to determine whether a file has grown since
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it was last read.
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The module defines the following:
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\begin{excdesc}{error}
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The exception raised when an error occurs. The accompanying value is
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a pair containing the numeric error code from \cdata{errno} and the
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corresponding string, as would be printed by the \C{} function
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\cfunction{perror()}.
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\end{excdesc}
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\begin{funcdesc}{select}{iwtd, owtd, ewtd\optional{, timeout}}
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This is a straightforward interface to the \UNIX{} \cfunction{select()}
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system call. The first three arguments are lists of `waitable
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objects': either integers representing \UNIX{} file descriptors or
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objects with a parameterless method named \method{fileno()} returning
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such an integer. The three lists of waitable objects are for input,
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output and `exceptional conditions', respectively. Empty lists are
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allowed. The optional \var{timeout} argument specifies a time-out as a
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floating point number in seconds. When the \var{timeout} argument
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is omitted the function blocks until at least one file descriptor is
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ready. A time-out value of zero specifies a poll and never blocks.
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The return value is a triple of lists of objects that are ready:
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subsets of the first three arguments. When the time-out is reached
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without a file descriptor becoming ready, three empty lists are
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returned.
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Amongst the acceptable object types in the lists are Python file
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objects (e.g. \code{sys.stdin}, or objects returned by
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\function{open()} or \function{os.popen()}), socket objects
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returned by \function{socket.socket()},%
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\withsubitem{(in module socket)}{\ttindex{socket()}}
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\withsubitem{(in module os)}{\ttindex{popen()}}
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and the module \module{stdwin}\refbimodindex{stdwin} which happens to
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define a function \function{fileno()}%
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\withsubitem{(in module stdwin)}{\ttindex{fileno()}}
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for just this purpose. You may
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also define a \dfn{wrapper} class yourself, as long as it has an
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appropriate \method{fileno()} method (that really returns a \UNIX{}
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file descriptor, not just a random integer).
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\end{funcdesc}
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