defer-11.py

from twisted.internet.defer import Deferred

print("""\
This example illustrates how deferreds can
be fired before they are returned. First we
make a new deferred, fire it, then add some
callbacks.
""")

# three simple callbacks

def callback_1(res):
    print('callback_1 got', res)
    return 1

def callback_2(res):
    print('callback_2 got', res)
    return 2

def callback_3(res):
    print('callback_3 got', res)
    return 3

# We create a deferred and fire it immediately:
d = Deferred()

print('Firing empty deferred.')
d.callback(0)

# Now we add the callbacks to the deferred.
# Notice how each callback fires immediately.

print('Adding first callback.')
d.addCallback(callback_1)

print('Adding second callback.')
d.addCallback(callback_2)

print('Adding third callback.')
d.addCallback(callback_3)

print("""
Because the deferred was already fired, it
invoked each callback as soon as it was added.

Now we create a deferred and fire it, but
pause it first with the pause() method.
""")

# We do the same thing, but pause the deferred:

d = Deferred()
print('Pausing, then firing deferred.')
d.pause()
d.callback(0)

print('Adding callbacks.')
d.addCallback(callback_1)
d.addCallback(callback_2)
d.addCallback(callback_3)

print('Unpausing the deferred.')
d.unpause()