python answers please

Write a recursive function, substring (stri, str2), that returns true if str2 is a substring in stri. If str2 is not a substring in stri then the function should return false. For example, substring("Jeffery", "Jeff") returns true and substring("pillow", "mat") returns false. The function should be case sensitive, thus, substring("Jeffery". "jeff") returns false. If either input string is an empty string then the function should return false. A correct solution does not use the membership operators in or not in or the string method find()