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selectselect available in
most UNIX versions. It defines the following:
errno and the
corresponding string, as would be printed by the C function
perror().
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 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 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 posix.popen()), socket objects returned by
socket.socket(), and the module stdwin which happens to
define a function fileno() for just this purpose. You may
also define a wrapper class yourself, as long as it has an
appropriate fileno() method (that really returns a UNIX file
descriptor, not just a random integer).