Detect period of unknown source

Question

How to detect repeating digits in an infinite sequence? I tried Floyd & Brent detection algorithm but come to nothing... I have a generator that yields

Answer 1

I have no idea about proper algorithms to apply here, but my understanding also is that you can never know for sure that you've detected a period if you have consumed only a finite number of terms. Anyway, here's what I've come up with, this is a very naive implementation, more to educate from the comments than to provide a good solution (I guess).

def guess_period(source, minlen=1, maxlen=100, trials=100):
    for n in range(minlen, maxlen+1):
        p = [j for i, j in zip(range(n), source)]
        if all([j for i, j in zip(range(n), source)] == p
               for k in range(trials)):
            return tuple(p)
    return None

This one, however, "forgets" the initial order and returns a tuple that is a cyclic permutation of the actual period:

In [101]: guess_period(gen)
Out[101]: (0, 1, 4, 8, 2, 1, 3, 3, 1, 1)

To compensate for this, you'll need to keep track of the offset.