Online average using coroutine

coroutine_online_average.py

import functools
import itertools


def coroutine_send(func):
    @functools.wraps(func)
    def start(*args, **kwds):
        cr = func(*args, **kwds)
        next(cr)
        return cr.send
    return start


@coroutine_send
def online_average():
    """
    Online average calculator.

    >>> avgr = online_average()
    >>> for i in range(3):
    ...     a = avgr(i)
    ...     print(a)
    ...
    0
    0.5
    1.0
    >>> a == sum(range(3)) / 3
    True

    """
    s = yield
    for n in itertools.count(2):
        s = (yield s) / n + s * (n - 1) / n