How can I tell if a string repeats itself in Python?

Question

I\'m looking for a way to test whether or not a given string repeats itself for the entire string or not.

Examples:

[
    \'0045662100456621004566210         


        

Answer 1

First, halve the string as long as it's a "2 part" duplicate. This reduces the search space if there are an even number of repeats. Then, working forwards to find the smallest repeating string, check if splitting the full string by increasingly larger sub-string results in only empty values. Only sub-strings up to length // 2 need to be tested since anything over that would have no repeats.

def shortest_repeat(orig_value):
    if not orig_value:
        return None

    value = orig_value

    while True:
        len_half = len(value) // 2
        first_half = value[:len_half]

        if first_half != value[len_half:]:
            break

        value = first_half

    len_value = len(value)
    split = value.split

    for i in (i for i in range(1, len_value // 2) if len_value % i == 0):
        if not any(split(value[:i])):
            return value[:i]

    return value if value != orig_value else None

This returns the shortest match or None if there is no match.