alexei

if True:
    from multiprocessing import Process as Worker, Queue
else:
    from threading import Thread as Worker
    from Queue import Queue

from time import sleep

class Memoize(object):
    "Cache results of a function."

    def __init__(self, f):
        self.f = f
        self.dict = {}

    def __call__(self, x):
        if x not in self.dict:
            self.dict[x] = self.f(x)

        return self.dict[x]

def func(x):
    print "ENTERED: func(", x, ")"
    return x**2

func = Memoize(func)

def pmap(f, xs):
    """Map variant:

        >>> def f(x):
        ...     sleep(1)
        ...     return 10 * x

        >>> xs = range(1, 10)

        >>> pmap(f, xs)
        [10, 20, 30, 40, 50, 60, 70, 80, 90]

    This would sleep 9 times as long:

#       >>> map(f, xs)
#       [10, 20, 30, 40, 50, 60, 70, 80, 90]

    """

    # will return this as a result:
    results = [None] * len(xs)

    def work(q, i, x):
        # compute the result and post it together with identifier:
        q.put((i, f(x)))

    # here the workers will post results:
    q = Queue()

    # create thread/process objects, stay conservative pack everything
    # explicitly into args:
    workers = [ Worker(target=work, args=(q, i, x)) for i, x in enumerate(xs) ]

    # start all workers:
    for w in workers:
        w.start()

    # wait for completion:
    for w in workers:
        w.join()

        # another result must be ready, collect them:
        i, fxi = q.get()
        results[i] = fxi

    # now that "results" must have been set:
    return results

print "Call func(2) four times:"
print func(2)
print func(2)
print func(2)
print func(2)

print "Map func() over four 2's:"
print map(func, [2, 2, 2, 2])
print "Map func() over four 3's:"
print map(func, [3, 3, 3, 3])

print "ParMap func() over four 2's:"
print pmap(func, [2, 2, 2, 2])
print "ParMap func() over four 3's:"
print pmap(func, [3, 3, 3, 3])
print "ParMap func() over four 4's:"
print pmap(func, [4, 4, 4, 4])

# python pmap.py [-v]:
#   if __name__ == "__main__":
#       import doctest
#       doctest.testmod()

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