用户输入一个字符串作为密码，判断密码强度，规则为：密码长度小于8 为弱密码，密码长度大于等于8且包含至少2 种字符为中等强度;密码包含3 种字符为强;包含全部4 种字符为极强。

可以编写一个Python函数来实现这个密码强度的判断。下面是一个简单的函数，它接收一个字符串作为输入并检查其长度和字符种类：

def password_strength(password):
    # 定义字符种类：数字、大写字母、小写字母和其他字符
    char_types = ['digit', 'upper', 'lower', 'special']

    # 初始化计数器
    digit_count = 0
    upper_count = 0
    lower_count = 0
    special_count = 0

    # 检查每个字符类型
    for char in password:
        if char.isdigit():
            digit_count += 1
        elif char.isupper():
            upper_count += 1
        elif char.islower():
            lower_count += 1
        else:
            special_count += 1

    # 判断密码强度
    if len(password) < 8:
        strength = "弱"
    elif len(password) >= 8 and digit_count + upper_count + lower_count > 1:
        strength = "中等强度" if special_count == 0 else "强"
    elif len(password) >= 8 and special_count == 3:
        strength = "极强"
    else:
        strength = "不符合规则"

    return strength

# 测试示例
passwords = ["short", "8char", "has1Special", "longPasswordWithAllChars"]
for p in passwords:
    print(f"{p}: {password_strength(p)}")