Find length of the Longest Prefix which is also Suffix

Returns length of the longest prefix which is also suffix
and the two do not overlap. This function mainly is a copy
of computeLPSArray(). See:
https://www.geeksforgeeks.org/searching-for-patterns-set-2-kmp-algorithm/

def longestPrefixSuffix(s):
    n = len(s)
    for res in range(n // 2, 0, -1):
        # Check for shorter lengths of first half
        prefix = s[0: res]
        suffix = s[n - res: n]
        if (prefix == suffix):
            return res
    # if no prefix and suffix match occurs
    return 0

def longestPrefixSuffix(s):
   n = len(s)
   lps = [0] * n               # lps[0] is always 0
   l = 0                       # length of the previous longest prefix suffix
   # the loop calculates lps[i] for i = 1 to n-1
   i = 1
   while (i < n):
       if (s[i] == s[l]):
           l = l + 1
           lps[i] = l
           i = i + 1
       else:
           # (pat[i] != pat[len])
           # This is tricky. Consider the example:
           #  AAACAAAA and i = 7.
           # The idea is similar to search step.
           if (l != 0):
               l = lps[l - 1]
               # Also, note that we do not increment i here
           else:
               # if (len == 0)
               lps[i] = 0
               i = i + 1
   res = lps[n - 1]

   # Since we are looking for non overlapping parts.
   if (res > n / 2):
       return n // 2
   else:
       return res

Test

txt = "AABAACAADAABAABA"
print(longestPrefixSuffix(txt))             # 4