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Install the docs (with fewer rules). Add descriptions for the system variables.
author Guido van Rossum <guido@python.org>
date Mon, 10 Apr 2000 19:36:27 +0000
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1 \section{\module{select} ---
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2 Waiting for I/O completion}
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3
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4 \declaremodule{builtin}{select}
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5 \modulesynopsis{Wait for I/O completion on multiple streams.}
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6
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7
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8 This module provides access to the function \cfunction{select()}
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9 available in most operating systems. Note that on Windows, it only
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10 works for sockets; on other operating systems, it also works for other
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11 file types (in particular, on \UNIX{}, it works on pipes). It cannot
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12 be used on regular files to determine whether a file has grown since
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13 it was last read.
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14
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15 The module defines the following:
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16
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17 \begin{excdesc}{error}
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18 The exception raised when an error occurs. The accompanying value is
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19 a pair containing the numeric error code from \cdata{errno} and the
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20 corresponding string, as would be printed by the \C{} function
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21 \cfunction{perror()}.
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22 \end{excdesc}
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23
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24 \begin{funcdesc}{select}{iwtd, owtd, ewtd\optional{, timeout}}
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25 This is a straightforward interface to the \UNIX{} \cfunction{select()}
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26 system call. The first three arguments are lists of `waitable
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27 objects': either integers representing \UNIX{} file descriptors or
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28 objects with a parameterless method named \method{fileno()} returning
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29 such an integer. The three lists of waitable objects are for input,
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30 output and `exceptional conditions', respectively. Empty lists are
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31 allowed. The optional \var{timeout} argument specifies a time-out as a
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32 floating point number in seconds. When the \var{timeout} argument
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33 is omitted the function blocks until at least one file descriptor is
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34 ready. A time-out value of zero specifies a poll and never blocks.
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35
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36 The return value is a triple of lists of objects that are ready:
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37 subsets of the first three arguments. When the time-out is reached
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38 without a file descriptor becoming ready, three empty lists are
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39 returned.
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40
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41 Amongst the acceptable object types in the lists are Python file
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42 objects (e.g. \code{sys.stdin}, or objects returned by
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43 \function{open()} or \function{os.popen()}), socket objects
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44 returned by \function{socket.socket()},%
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45 \withsubitem{(in module socket)}{\ttindex{socket()}}
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46 \withsubitem{(in module os)}{\ttindex{popen()}}
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47 and the module \module{stdwin}\refbimodindex{stdwin} which happens to
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48 define a function
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49 \function{fileno()}\withsubitem{(in module stdwin)}{\ttindex{fileno()}}
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50 for just this purpose. You may
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51 also define a \dfn{wrapper} class yourself, as long as it has an
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52 appropriate \method{fileno()} method (that really returns a \UNIX{}
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53 file descriptor, not just a random integer).
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54 \end{funcdesc}