The dangers of inlineCallbacks

results

$ time python /tmp/test_cb.py
done
done
done
done
done
python /tmp/test.py  0.05s user 0.01s system 6% cpu 1.065 total

$ time python /tmp/test_inline.py
done
done
done
done
done
python /tmp/test.py  0.04s user 0.01s system 1% cpu 5.056 total

test_cb.py

#!/usr/bin/env python

from __future__ import (absolute_import, division, print_function,
                        unicode_literals)

from twisted.internet import (reactor, defer)


def doSomething():
    d = defer.Deferred()
    reactor.callLater(1, d.callback, None)
    return d


def loop():
    for i in xrange(5):
        d = doSomething().addCallback(lambda _: print("done"))

    d.addCallback(lambda _: reactor.stop())


def main():
    loop()


if __name__ == '__main__':
    main()
    reactor.run()

test_inline.py

#!/usr/bin/env python

from __future__ import (absolute_import, division, print_function,
                        unicode_literals)

from twisted.internet import (reactor, defer)


def doSomething():
    d = defer.Deferred()
    reactor.callLater(1, d.callback, None)
    return d


@defer.inlineCallbacks
def loop():
    for i in xrange(5):
        yield doSomething()
        print("done")

    reactor.stop()


def main():
    loop()


if __name__ == '__main__':
    main()
    reactor.run()