python - Common substring of length k -

i'm trying write function gets 2 strings , integer 'k' , returns common substring of both strings of length k. (if there more 1, returns 1 @ random). there alot of algorithms online checks longest common substring found none checks k-length substring.

i think hash tables correct way if want optimized couldn't quite it.

i write function checks if there more 1 k-length sequence in list. here got:

def repeat(st, k):     in range(len(st) - k + 1):         j in range(i + 1, len(st) - k + 1):             if st[i : + k] == st[j : j + k]:                 return st[i : + k]     return false 

i appreciate this... :/

simple version this:

def common_substr(a, b, k):   substr in (a[i:i+k] in range(len(a)-k+1)):     if substr in b:       return substr 

i guess large input strings (e. g. megabytes of text) , large k might inefficient , building hashes of possible substrings of length k can improve speed:

def common_substr(a, b, k):   substrs = set(a[i:i+k] in range(len(a)-k+1))   substr in (b[i:i+k] in range(len(b)-k+1)):     if substr in substrs:       return substr 

but guess there cleverer algorithms around this. comparably simple strstr() (find string in string) has more efficient solutions straight-forward 1 can implement.