How to find longest repetitive sequence in a string in Python?

PythonServer Side ProgrammingProgramming

You can use defaultdict to tally each sub string beginning with each position in the input string. The getsubs method is a generator method that yields a smaller sub string every time it is called.

Example

from collections import defaultdict
def getsubs(loc, s):
    substr = s[loc:]
    i = -1
    while(substr):
        yield substr
        substr = s[loc:i]
        i -= 1
def longestRepetitiveSubstring(r):
    occ = defaultdict(int)
    # tally all occurrences of all substrings
    for i in range(len(r)):
        for sub in getsubs(i,r):
            occ[sub] += 1
    # filter out all sub strings with fewer than 2 occurrences
    filtered = [k for k,v in occ.items() if v >= 2]
    if filtered:
        maxkey =  max(filtered, key=len) # Find longest string
        return maxkey
    else:
        raise ValueError("no repetitions of any substring of '%s' with 2 or more occurrences" % (r))
longestRepetitiveSubstring("hellopeople18654randomtexthellopeoplefromallaroundthe world")

Output

This will give the output:

'hellopeople'
raja
Published on 14-Dec-2017 10:02:05
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