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(python2.1-lib.info)select

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Waiting for I/O completion
==========================

Wait for I/O completion on multiple streams.

This module provides access to the `select()' and `poll()' functions
available in most operating systems.  Note that on Windows, it only
works for sockets; on other operating systems, it also works for other
file types (in particular, on UNIX, it works on pipes).  It cannot be
used on regular files to determine whether a file has grown since it
was last read.

The module defines the following:

`error'
     The exception raised when an error occurs.  The accompanying value
     is a pair containing the numeric error code from `errno' and the
     corresponding string, as would be printed by the C function
     `perror()'.

`poll()'
     (Not supported by all operating systems.)  Returns a polling
     object, which supports registering and unregistering file
     descriptors, and then polling them for I/O events; see
     section~Note: threading below for the methods supported by
     polling objects.

`select(iwtd, owtd, ewtd[, timeout])'
     This is a straightforward interface to the UNIX `select()' system
     call.  The first three arguments are lists of `waitable objects':
     either integers representing file descriptors or objects with a
     parameterless method named `fileno()' returning such an integer.
     The three lists of waitable objects are for input, output and
     `exceptional conditions', respectively.  Empty lists are allowed,
     but acceptance of three empty lists is platform-dependent.  (It is
     known to work on UNIX but not on Windows.)  The optional TIMEOUT
     argument specifies a time-out as a floating point number in
     seconds.  When the 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. `sys.stdin', or objects returned by `open()' or
     `os.popen()'), socket objects returned by `socket.socket()', .
     You may also define a "wrapper" class yourself, as long as it has
     an appropriate `fileno()' method (that really returns a file
     descriptor, not just a random integer).  *Note:*   File objects on
     Windows are not acceptable, but sockets are.  On Windows, the
     underlying `select()' function is provided by the WinSock library,
     and does not handle file desciptors that don't originate from
     WinSock.

Polling Objects