# cpython / Doc / libselect.tex

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 \section{Built-in module \sectcode{select}} \bimodindex{select} This module provides access to the function \code{select} available in most \UNIX{} versions. It defines the following: \renewcommand{\indexsubitem}{(in module select)} \begin{excdesc}{error} The exception raised when an error occurs. The accompanying value is a pair containing the numeric error code from \code{errno} and the corresponding string, as would be printed by the C function \code{perror()}. \end{excdesc} \begin{funcdesc}{select}{iwtd\, owtd\, ewtd\, timeout} This is a straightforward interface to the \UNIX{} \code{select()} system call. The first three arguments are lists of waitable objects': either integers representing \UNIX{} file descriptors or objects with a parameterless method named \code{fileno()} returning such an integer. The three lists of waitable objects are for input, output and exceptional conditions', respectively. Empty lists are allowed. The optional last argument is a time-out specified as a 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 objects (e.g. \code{sys.stdin}, or objects returned by \code{open()} or \code{posix.popen()}), socket objects returned by \code{socket.socket()}, and the module \code{stdwin} which happens to define a function \code{fileno()} for just this purpose. You may also define a \dfn{wrapper} class yourself, as long as it has an appropriate \code{fileno()} method (that really returns a \UNIX{} file descriptor, not just a random integer). \end{funcdesc} \ttindex{socket} \ttindex{stdwin}