Python finding repeating sequence in list of integers?

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Guess the sequence length by iterating through guesses between 2 and half the sequence length. If no pattern is discovered, return 1 by default.

def guess_seq_len(seq):
    guess = 1
    max_len = len(seq) / 2
    for x in range(2, max_len):
        if seq[0:x] == seq[x:2*x] :
            return x

    return guess

list_a = [111,0,3,1,111,0,3,1,111,0,3,1] 
list_b = [67,4,67,4,67,4,67,4,2,9,0]
list_c = [1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6,7,8,9,0,23,18,10]

print guess_seq_len(list_a)
print guess_seq_len(list_b)
print guess_seq_len(list_c)
print guess_seq_len(range(500))   # test of no repetition

This gives (as expected):

4
2
10
1

As requested, this alternative gives longest repeated sequence. Hence it will return 4 for list_b. The only change is guess = x instead of return x

def guess_seq_len(seq):
    guess = 1
    max_len = len(seq) / 2
    for x in range(2, max_len):
        if seq[0:x] == seq[x:2*x] :
            guess = x

    return guess

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