Python Learning(5) if语句

水深无声 2022-04-24 07:38 145阅读 0赞

python编程从入门到实践

# -*- coding: utf-8 -*-
    """ chapter5 if语句 """
    # 5.1 一个简单示例
    cars = ['audi', '漏油benz', 'bmw', 'toyota']
    for car in cars:
        if car == 'bmw':  # 判断字符串字面量相等
            print(car.upper())
        else:
            print(car.title())
    
    # 5.2 条件测试 :每条if语句的核心都是一个值为True或False的表达式，这种表达式被称为条件测试。
    # 5.2.1 检查是否相等
    car = 'bmw'
    print(car == 'bmw')  # true
    
    # 5.2.2 检查是否相等时不考虑大小写
    # 在Python中检查是否相等时区分大小写
    car = 'Audi'
    print(car == 'audi')  # False
    
    # 5.2.3 检查是否不相等 :要判断两个值是否不等，可结合使用惊叹号和等号（!=）
    name = '李四'
    if name == '张三':
        print('你是张三')
    else:
        print('你不是张三')
    
    # 5.2.4 比较数字
    answer = 17
    if answer != 42:
        print('你的答案是错误的,宇宙的终极秘密是42,不是%s!' % answer)
    else:
        print('你看破了宇宙!!!')
    
    # 5.2.5 检查多个条件
    # 1. 使用and检查多个条件
    age = 10
    if age < 30 and age < 40:
        print("aa")
    else:
        print("bb")
    
    if (age < 50) & (age < 60):
        print("cc")
    else:
        print("dd")
    
    # 2. 使用or检查多个条件
    age_1 = 20
    if (age_1 > 10) | (age_1 > 15):
        print("ee")
    else:
        print("ff")
    
    # 5.2.6 检查特定值是否包含在列表中 in
    grade = ['甲', '乙', '丙']
    mina = '丁'
    if min in grade:
        print('good-level')
    else:
        print('bad-level')
    
    # 5.2.7 检查特定值是否不包含在列表中 not in
    grade = ['甲', '乙', '丙']
    zhao_level = '丁'
    if zhao_level not in grade:
        print('bad-level')
    else:
        print('good-level')
    
    # 5.2.8 布尔表达式
    # True/False
    
    # 5.3 if 语句
    # 5.3.1 简单的 if 语句
    age = 19
    if age >= 18:
        print("You are old enough to vote!")
    
    # 5.3.2 if-else 语句
    age = 17
    if age >= 18:
        print("You are old enough to vote!")
        print("Have you registered to vote yet?")
    else:
        print("Sorry, you are too young to vote.")
        print("Please register to vote as soon as you turn 18!")
    
    # 5.3.3 if-elif-else 结构
    age = 12
    if age < 4:
        print("Your admission cost is $0.")
    elif age < 18:
        print("Your admission cost is $5.")
    else:
        print("Your admission cost is $10.")
    
    age = 12
    if age < 4:
        price = 0
    elif age < 18:
        price = 5
    else:
        price = 10
    print("Your admission cost is $" + str(price) + ".")
    
    # 5.3.4 使用多个 elif 代码块
    age = 12
    price
    if age < 4:
        price = 0
    elif age < 18:
        price = 10
    elif age < 65:
        price = 20
    else:
        price = 10
    print("Your admission cost is $" + str(price) + ".")
    
    # 5.3.5 省略 else 代码块
    # Python并不要求if-elif结构后面必须有else代码块:else是一条包罗万象的语句，只要不满足任何if或elif中的条件测试，其中的代码就会执行，
    # 这可能会引入无效甚至恶意的数据。如果知道最终要测试的条件，应考虑使用一个elif代码块来代替else代码块。
    
    # 5.3.6 测试多个条件
    request_word = ['花', '好', '月', '圆']
    need_words = ['花', '好', '月', '圆']
    finish_words = []
    for need_word in need_words:
        if need_word in request_word:
            print("need %s" % need_word)
            finish_words.append(need_word)
    print("GOOD" if len(finish_words) > 2 else "BAD")  # python中没有三元运算符，可以用这种格式替代
    
    # 5.4 使用 if 语句处理列表
    # 5.4.1 检查特殊元素
    requested_toppings = ['mushrooms', 'green peppers', 'extra cheese']
    for requested_topping in requested_toppings:
        print("Adding " + requested_topping + ".")
    print("\nFinished making your pizza!")
    requested_toppings = ['mushrooms', 'green peppers', 'extra cheese']
    for requested_topping in requested_toppings:
        if requested_topping == 'green peppers':
            print("Sorry, we are out of green peppers right now.")
        else:
            print("Adding " + requested_topping + ".")
    print("\nFinished making your pizza!")
    
    # 5.4.2 确定列表不是空的
    requested_toppings = []
    if requested_toppings:
        for requested_topping in requested_toppings:
            print("Adding " + requested_topping + ".")
        print("\nFinished making your pizza!")
    else:
        print("Are you sure you want a plain pizza?")
    
    # 5.4.3 使用多个列表
    available_words = ['小', '英', '雄', '雨', '来']
    request_words = ['小', '英', '雄', '哪', '吒']
    for request_word in request_words:
        if request_word in available_words:
            print('我们有这个word：%s' % request_word)
        else:
            print('我们么有这个word:%s' % request_word)
    
    # 5.5 设置 if 语句的格式
    # PEP 8提供的唯一建议是，在诸如==、 >=和<=等比较运算符两边各添加一个空格，例如， if age < 4:要比if age<4:好