cpython/Doc/lib/libselect.tex

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\section{Built-in Module \module{select}}
\label{module-select}
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\bimodindex{select}
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This module provides access to the function \cfunction{select()}
available in most \UNIX{} versions. It defines the following:
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\begin{excdesc}{error}
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
corresponding string, as would be printed by the \C{} function
\cfunction{perror()}.
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\end{excdesc}
\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
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,
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
is omitted the function blocks until at least one file descriptor is
ready. A time-out value of zero specifies a poll and never blocks.
The return value is a triple of lists of objects that are ready:
subsets of the first three arguments. When the time-out is reached
without a file descriptor becoming ready, three empty lists are
returned.
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
\function{open()} or \function{os.popen()}), socket objects
returned by \function{socket.socket()},%
\withsubitem{(in module socket)}{\ttindex{socket()}}
\withsubitem{(in module posix)}{\ttindex{popen()}}
\withsubitem{(in module os)}{\ttindex{popen()}}
and the module \module{stdwin}\refbimodindex{stdwin} which happens to
define a function \function{fileno()}%
\withsubitem{(in module stdwin)}{\ttindex{fileno()}}
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{}
file descriptor, not just a random integer).
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\end{funcdesc}