獲取一個類的所有子類
代碼如下:
def itersubclasses(cls, _seen=None):
    """Generator over all subclasses of a given class in depth first order."""
    if not isinstance(cls, type):
        raise TypeError(_('itersubclasses must be called with '
                          'new-style classes, not %.100r') % cls)
    _seen = _seen or set()
    try:
        subs = cls.__subclasses__()
    except TypeError:   # fails only when cls is type
        subs = cls.__subclasses__(cls)
    for sub in subs:
        if sub not in _seen:
            _seen.add(sub)
            yield sub
            for sub in itersubclasses(sub, _seen):
                yield sub

簡單的線程配合
代碼如下:
import threading
is_done = threading.Event()
consumer = threading.Thread(
    target=self.consume_results,
    args=(key, self.task, runner.result_queue, is_done))
consumer.start()
self.duration = runner.run(
        name, kw.get("context", {}), kw.get("args", {}))
is_done.set()
consumer.join() #主線程堵塞，直到consumer運行結束

多說一點，threading.Event()也可以被替換為threading.Condition()，condition有notify(), wait(), notifyAll()。解釋如下：
代碼如下:
The wait() method releases the lock, and then blocks until it is awakened by a notify() or notifyAll() call for the same condition variable in another thread. Once awakened, it re-acquires the lock and returns. It is also possible to specify a timeout.
The notify() method wakes up one of the threads waiting for the condition variable, if any are waiting. The notifyAll() method wakes up all threads waiting for the condition variable.
Note: the notify() and notifyAll() methods don't release the lock; this means that the thread or threads awakened will not return from their wait() call immediately, but only when the thread that called notify() or notifyAll() finally relinquishes ownership of the lock.

代碼如下:
# Consume one item
cv.acquire()
while not an_item_is_available():
    cv.wait()
get_an_available_item()
cv.release()
# Produce one item
cv.acquire()
make_an_item_available()
cv.notify()