Shortest Repeating Sub-String

Question

I am looking for an efficient way to extract the shortest repeating substring. For example:

input1 = \'dabcdbcdbcdd\'
ouput1 = \'bcd\'

input2 = \'cbabababac         


        

Answer 1

^ matches at the start of a string. In your example the repeating substrings don't start at the beginning. Similar for $. Without ^ and $ the pattern .*? always matches empty string. Demo:

import re

def srp(s):
    return re.search(r'(.+?)\1+', s).group(1)

print srp('dabcdbcdbcdd') # -> bcd
print srp('cbabababac')   # -> ba

Though It doesn't find the shortest substring.