Python

Python 编程从入门到实践-chapter5

Posted by franki on March 4, 2024

if 语句

一个简单的示例

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

条件测试

检查是否相等

car == 'bmw'

输出 True

比较相等时忽略大小写

car.lower() == 'audi'

输出 True

检查是否不等

requested_topping = 'mushrooms'
if requested_topping != 'anchovies':
    print('Hold the anchovies!')

输出 Hold the anchovies!

数值比较

age == 8

age < 8

age > 8

age != 8

检查多个条件

age > 8 and age < 20
age > 8 or age < 20

检查特定的值是否在/不在列表中

requested_toppings = ['mushrooms', 'onions', 'pineapple']
'mushrooms' in requested_toppings

'mushrooms' not in requested_toppings

输出 True

布尔表达式

game_active = True
can_edit = False

if 语句

简单的 if 语句

if conditional_test:
    do_something

if-else 语句

if conditional_test:
    do_something
else:
    do_other_thing

if-elif-else 语句

if conditional_test:
    do_something
elif another_canditional_test:
    do_another_thing
elif another_canditional_test:
    do_another_thing
elif another_canditional_test:
    do_another_thing
elif another_canditional_test:
    do_another_thing
else:
    do_other_thing

多个条件

if conditional_test:
    do_something

if another_canditional_test:
    do_another_thing

if another_canditional_test:
    do_another_thing

使用 if 语句处理列表

检查特殊元素

requested_toppings = ['mushrooms', 'onions', 'pineapple']

for requested_topping in requested_toppings:
    if requested_topping == 'mushrooms':
        print('Sorry, we are out of mushrooms right now.')
    else:
        print(f'Adding {requested_topping}.')

输出 Sorry, we are out of mushrooms right now. Adding onions. Adding pineapple.

确定非空

requested_toppings = ['mushrooms', 'onions', 'pineapple']

if requested_toppings:
    for requested_topping in requested_toppings:
        if requested_topping == 'mushrooms':
            print('Sorry, we are out of mushrooms right now.')
        else:
            print(f'Adding {requested_topping}.')

使用多个列表

available_toppings = ['mushrooms', 'onions', 'pineapple']
requested_toppings = ['mushrooms', 'extra cheese']

for requested_topping in requested_toppings:
    if requested_topping in available_toppings:
        print(f'Adding {requested_topping}.')
    else:
        print(f'Sorry, we are out of {requested_topping} right now.')
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