Python if语句

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（1）简单的if语句

cars = ['audi', 'bmw', 'subaru', 'toyota']
for car in cars:
    if car == 'bmw':
        print(car.upper()) 
    else:
        print(car.title())

输出

Audi
BMW
Subaru
Toyota

（2）and or

age_0 = 22
age_1 = 24
if(age_0 >= 21 and age_1 >= 21):
    print("Yes1")
if(age_0 >= 24 or age_1 >= 24):
    print("Yes2")

输出

Yes
Yes2

（3）检查特定值是否包含在列表中

requested_toppings = ['mushrooms', 'onions', 'pineapple']
if('mushrooms' in requested_toppings):
    print("包含1")
if('pepperoni' in requested_toppings):
    print("包含2")

输出

包含1

（4）检查特定值是否不包含在列表中

banned_users = ['andrew', 'carolina', 'david']
user = 'marie'
if user not in banned_users:
    print(user.title() + ", you can post a response if you wish.")

输出

Marie, you can post a response if you wish.

（5）布尔表达式

game_active = True
can_edit = False

（6）if-elif-else 结构

age = 12
if age < 4:
    price = 0
elif age < 18:
    price = 5
else:
    price = 10
print("Your admission cost is $" + str(price) + ".")

输出

Your admission cost is $5.

（7）测试多个条件

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!")

输出

Adding mushrooms.
Adding extra cheese.

Finished making your pizza!

（8）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?")

输出

Are you sure you want a plain pizza?

（9）使用多个列表

available_toppings = ['mushrooms', 'olives', 'green peppers',
'pepperoni', 'pineapple', 'extra cheese']
requested_toppings = ['mushrooms', 'french fries', 'extra cheese']
for requested_topping in requested_toppings:
    if requested_topping in available_toppings:
        print("Adding " + requested_topping + ".")
    else:
        print("Sorry, we don't have " + requested_topping + ".")
print("\nFinished making your pizza!")

输出

Adding mushrooms.
Sorry, we don't have french fries.
Adding extra cheese.

Finished making your pizza!