Python standard library: selectors

Check for available classes (selectors)

import selectors

for c in ['SelectSelector', 'PollSelector', 'EpollSelector', 'DevpollSelector', 'KqueueSelector']:
    print(f"{c:<15} is {'not' if not hasattr(selectors, c) else '   '} available")

Default selector

>>> import selectors
>>> selectors.DefaultSelector().__class__
<class 'selectors.EpollSelector'>

Simple echo server

import socket
import selectors

sel = selectors.DefaultSelector()

def accept(sock, mask):
    conn, addr = sock.accept()  # Should be ready
    print('accepted', conn, 'from', addr)
    conn.setblocking(False)
    sel.register(conn, selectors.EVENT_READ, read)

def read(conn, mask):
    data = conn.recv(1000)  # Should be ready
    if data:
        print('echoing', repr(data), 'to', conn)
        conn.send(data)  # Hope it won't block
    else:
        print('closing', conn)
        sel.unregister(conn)
        conn.close()

sock = socket.socket()
sock.bind(('localhost', 1234))

# puts the socket into listening mode and
# allow up to 42 pending connection requests
# to wait in the operating system’s connection queue.
sock.listen(42)

sock.setblocking(False)

#
# Monitor sock for EVENT_READ (which indicates
# a new connection request here?)
# The third argument can be any object and is returned
# as key.data in the loop below.
# 
sel.register(sock, selectors.EVENT_READ, accept)

while True:
    events = sel.select()
    for key, mask in events:
        callback = key.data
        callback(key.fileobj, mask)

See also