Python基础学习笔记第四章——if语句

一、简单示例

#简单示例1
cars = ['audi','bmw','subaru','toyota']
for car in cars:
    if car == 'bmw': 
    #注：两个等号是发问（必须是俩等号）                                                                      
        print(car.upper())
    else:
        print(car.title())

#输出Audi
#BMW
#Subaru
#Toyota                                                                                                                                                                                                                                      

二、if 语句

1. if 语句

代码如下（示例）：

age = 19
if age >= 18:
    print("You are old enough to vote!")
#输出You are old enough to vote!                                                                                                             

2. if-else语句

age = 19
if age >= 18:
    print("You are old enough to vote!")
else:
     print("Sorry,you are too young to vote.")
#输出You are old enough to vote!                                                                                                              

3. if-elif-else结构

age = 12
if age < 4:
    print("Your admission cast is 0")
elif age < 18:
    print("Your admission cast is 25")
else:
    print("Your admission cast is 40") 
#输出为Your admission cast is 25                                                                                                              

4. 使用elif代码块

age = 12
if age < 4:
    price = 0
elif age < 18:
    price = 25
elif age < 65:
    price = 40
else:    
#注：最后结尾用else，不能用elif                                                                                        
    price = 20
 print(price)
#输出为25                                                                                                              

5. 使用if语句处理列表

availiable_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 availiable_toppings:
        print(f"Adding {requested_topping}.")
    else:
        print(f"Sorry,we do not have {requested_topping}.")
#输出Adding mushrooms.
#Sorry,we do not have french fries.
#Adding extra cheese.