1.11. select — Waiting for I/O completion

This module provides access to the poll() function available in most operating systems. It only works for the Simba channels; events, queues and sockets.


Returns a polling object, which supports registering and unregistering channels, and then polling them for I/O events.

class select.poll

The poll class.

>>> from sync import Queue
>>> poll = select.poll()
>>> queue = Queue()
>>> poll.register(queue)
>>> poll.poll(1.0)             # Timeout since no data is available in the queue.
>>> queue.write(b'hello')
>>> poll.poll()                # Data is available in the queue.
[(<0x20034050>, 1)]
>>> poll.poll()[0][0].read(5)  # Read the available data.
register(channel[, eventmask])

Register given channel with the polling object. Future calls to the poll() method will then check whether the channel has any pending I/O events.

eventmask is an optional bitmask describing the type of events you want to check for, and can be currently only be POLLIN.

Registering a file descriptor that’s already registered is not an error, and has the same effect as registering the descriptor exactly once.


Remove given channel being tracked by a polling object.

Attempting to remove a file descriptor that was never registered causes a KeyError exception to be raised.

modify(channel, eventmask)

Modifies an already registered channel. This has the same effect as register(channel, eventmask). Attempting to modify a channel that was never registered causes an IOError exception with errno ENOENT to be raised.


Polls the set of registered channels, and returns a possibly-empty list containing (channel, event) 2-tuples for the descriptors that have events or errors to report. An empty list indicates that the call timed out and no channel had any events to report. If timeout is given, it specifies the length of time in seconds which the system will wait for events before returning. If timeout is omitted, negative, or None, the call will block until there is an event for this poll object.


There is data to read.


Hung up.