如何在Python中使用哈希字符串匹配算法

def hash_string(s):
    """将字符串s转换为哈希值"""
    h = 0
    for c in s:
        h = (h * 31 + ord(c)) % 2**32
    return h

def find_substring(s, sub):
    """在字符串s中查找子串sub，返回子串的位置，如果没有找到返回-1"""
    n = len(sub)
    sub_hash = hash_string(sub)
    for i in range(len(s) - n + 1):
        if hash_string(s[i:i+n]) == sub_hash and s[i:i+n] == sub:
            return i
    return -1

# 示例
s = "pidancode.com is a great website for learning programming"
sub = "pidancode"
pos = find_substring(s, sub)
if pos == -1:
    print("没有找到子串")
else:
    print("子串在位置", pos)