#5.1 if语句的简单示例 ##示例： cars=['audi','bmw','subaru','toyota'] for car in cars:     if car=='bmw':         print(car.upper())     else:         print(car.title()) #5.2 if语句 ##if-else语句 ###示例： 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!")
##if-elif-else结构 ##用于检查超过两个的情形 ###示例： ''' 我们以一个根据年龄收费的游乐场为例： 4岁以下免费 4~18岁收费25美元 18（含）岁以上收费40美元 ''' age=12 if age <4:     print("Your admission cost is $0") elif age < 18:                              #只会执行通过测试的代码     print("Your admission cost is $25") else:     print("Your admission cost is $40")
###现在我们将上面的代码进行简化 age =12 if age <4:     price=0 elif age <18:     price=25 else:     price=40 print(f"Your admission cost is ${price}.") ###else代码块可以省略，只要不满足if或elif的测试条件，else中的代码就会执行 ###如果知道最终要测试的条件，就可以考虑用一个elif代码块代替else代码块 ###if-elif-else结构功能强大，但仅适合用于只有一个条件满足的情况，遇到了通过测试的情况，剩下的代码就会跳过执行
##测试多个条件 ###示例： requested_toppings=['mushrooms','extra cheese'] if 'mushrooms' in requested_toppings:     print('Adding mushrooms.') if 'pepperoni' in requested_toppings:     print('Adding pepperoni.') if 'extra cheese' in requested_toppings:     print('Adding extra cheese.')
print("\nFinished making your pizza!") ###首先创建一个列表，然后依次检查某一元素是否在列表中最后输出结果 ##如果只想执行一个代码块，就是用if-elif-else结构；如果要执行多个代码块，使用一系列独立的if语句
#5.3使用if语句检查列表 ##检查特殊元素 ###示例： requested_toppings=['nushrooms','green peppers','extra cheese'] for requested_topping in requested_toppings:     if requested_topping == 'green peppers':         print("Soory we are out of green peppers!")     else:         print(f"Adding {requested_topping}") print(f"\nFinished making your pizza!")
##确定列表不是空的 ##运行for循环前确定列表是否为空很重要 ###示例： requested_toppings=[] if requested_toppings:     for requested_topping in requested_toppings:         print(f"Adding {requested_topping}")     print ("\nFinished making your piaaz!") else:     print("Are you sure want a plain pizza?")
##使用多个列表： ###示例： available_toppings = ['mushrooms','olives','green peppers','pepperoni','pineapple','extra cheese'] requested_toppings = ['mushrooms','french fris','extra cheese'] for requested_topping in requested_toppings:     if requested_topping in available_toppings:         print(f"Adding {requested_topping}")     else:         print(f"Sorry,we don't have {requested_topping}") print("\nFinished making your pizza!")