Python编程 从入门到实践-5if语句上

笔记出处(学习UP主视频记录) https://www.bilibili.com/video/av35698354?p=8

5.1 一个简单示例

5.2 条件测试

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

Audi
BMW
Subaru
Toyota

5.2.1 检查是否相等

car = 'bmw'
print (car == 'bmw')

True

car = 'audi'
print (car == 'bmw')

False

5.2.2 检查是否相等时不考虑大小写

#两个大小写不同的值会被视为不相等
car = 'Audi'
print (car == 'audi')

False

car = 'Audi'
print (car.lower() == 'audi')

True

5.2.3 检查是否不相等

requested_toppong = 'mushrooms'

if requested_toppong != 'anchovies':
    print ("Hold the anchovies!")

Hold the anchovies!

5.2.4 比较数字

age = 18
print (age == 18)

True

answer = 17
if answer != 42:
    print ("That is not the correct answer. Please try again!")

That is not the correct answer. Please try again!

5.2.5 检查多个条件

1. 使用and检查多个条件

#检查是否2个人都不小于21岁
age_0 = 22
age_1 = 18

print (age_0 >= 21 and age_1 >= 21)

False

#检查是否2个人都不小于21岁
age_0 = 22
age_1 = 18

print (age_0 >= 21 and age_1 >= 21)

age_1 = 22
print (age_0 >= 21 and age_1 >= 21)

False
True

#检查是否2个人都不小于21岁
age_0 = 22
age_1 = 18

print ((age_0 >= 21) and (age_1 >= 21))

False

2. 使用or检查多个条件

#只要至少有1个条件满足，就能通过测试
#2个测试都没有通过时，表达式结果为False
age_0 = 22
age_1 = 18

print ((age_0 >= 21) or (age_1 >= 21))

True

age_0 = 22
age_1 = 18

age_0 = 18
print ((age_0 >= 21) or (age_1 >= 21))

False

5.2.6 检查特定值是否包含在列表中

requested_toppings = ['mushrooms', 'onions', 'pineapple']
print ('mushrooms' in requested_toppings)

True

requested_toppings = ['mushrooms', 'onions', 'pineapple']
print ('pepperoni' in requested_toppings)

False

5.2.7 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.")

Marie. you can post a response if you wish.

5.2.8 布尔表达式

True False

Caesar卢尚宇

2020年3月12日