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author Guido van Rossum <guido@python.org>
date Tue, 02 Dec 1997 20:38:11 +0000
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1 \section{Built-in Module \sectcode{select}}
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2 \label{module-select}
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3 \bimodindex{select}
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4
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5 This module provides access to the function \code{select} available in
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6 most \UNIX{} versions. It defines the following:
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7
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8 \renewcommand{\indexsubitem}{(in module select)}
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9 \begin{excdesc}{error}
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10 The exception raised when an error occurs. The accompanying value is
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11 a pair containing the numeric error code from \code{errno} and the
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12 corresponding string, as would be printed by the C function
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13 \code{perror()}.
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14 \end{excdesc}
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15
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16 \begin{funcdesc}{select}{iwtd\, owtd\, ewtd\optional{\, timeout}}
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17 This is a straightforward interface to the \UNIX{} \code{select()}
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18 system call. The first three arguments are lists of `waitable
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19 objects': either integers representing \UNIX{} file descriptors or
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20 objects with a parameterless method named \code{fileno()} returning
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21 such an integer. The three lists of waitable objects are for input,
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22 output and `exceptional conditions', respectively. Empty lists are
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23 allowed. The optional \var{timeout} argument specifies a time-out as a
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24 floating point number in seconds. When the \var{timeout} argument
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25 is omitted the function blocks until at least one file descriptor is
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26 ready. A time-out value of zero specifies a poll and never blocks.
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27
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28 The return value is a triple of lists of objects that are ready:
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29 subsets of the first three arguments. When the time-out is reached
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30 without a file descriptor becoming ready, three empty lists are
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31 returned.
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32
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33 Amongst the acceptable object types in the lists are Python file
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34 objects (e.g. \code{sys.stdin}, or objects returned by \code{open()}
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35 or \code{posix.popen()}), socket objects returned by
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36 \code{socket.socket()}, and the module \code{stdwin} which happens to
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37 define a function \code{fileno()} for just this purpose. You may
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38 also define a \dfn{wrapper} class yourself, as long as it has an
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39 appropriate \code{fileno()} method (that really returns a \UNIX{} file
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40 descriptor, not just a random integer).
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41 \end{funcdesc}
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42 \ttindex{socket}
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43 \ttindex{stdwin}