如何将子串替换为int

def replace_substring_with_int(string, substring, replacement):
    # 将原始字符串转换为字符数组
    chars = list(string)
    # 计算子串长度
    sub_len = len(substring)
    # 初始化起始位置
    start = 0
    # 循环遍历字符数组
    while start < len(chars):
        # 找到子串的位置
        index = string.find(substring, start)
        if index == -1:
            break
        # 替换子串为int值
        chars[index:index+sub_len] = str(replacement)
        # 更新起始位置
        start = index + sub_len
    # 将字符数组转换回字符串形式
    replaced_string = ''.join(chars)
    return replaced_string

# 示例用法
original_string = "abc123def456"
substring = "123"
replacement = 999
replaced_string = replace_substring_with_int(original_string, substring, replacement)
print(replaced_string)