I want to see if ending of one string is similar to starting of another string

if i have a string a="12345678" and b="56789" i want to update a as 123456789

these two strings are in a list

s="12345678"
b="56789"

o/p:

s=123456789

This works for me:

s="12345678"
b="56789"
for i in range(len(s)):if s[i] == b[0]:if s[i::] in b[0:len(s[i::])]:print('Found')

This works even if the string s repeats. What I am doing is going around, for the length of s and then seeing if s[i] is equal to the first char in b. I then look to see if the rest of s is, either b or is in b.