[TOC]
*****
# 5.1 一个简单示例
```
if car == 'bmw':
print(car.upper())
```
## 5.2.5 检查多个条件
**1. 使用and检查多个条件**
```
age_0 >= 21 and age_1 >= 21
```
**2. 使用or检查多个条件**
```
age_0 >= 21 or age_1 >= 21
```
## 5.2.6 检查特定值是否包含在列表中
```
requested_toppings = ['mushrooms', 'onions', 'pineapple']
'mushrooms' in requested_toppings
#True
```
## 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.")
```
## 5.2.8 布尔表达式
game_active = True
# 5.3 if 语句
## 5.3.1 简单的 if 语句
```
if age >= 18:
print("You are old enough to vote!")
```
## 5.3.2 if-else 语句
```
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!")
```
## 5.3.3 if-elif-else 结构
```
if age < 4:
price = 0
elif age < 18:
price = 5
elif age < 65:
price = 10
elif age >= 65:
price = 5
```
## 5.3.4 使用多个 elif 代码块
可以在最后省略else
```
if age < 4:
price = 0
elif age < 18:
price = 5
elif age < 65:
price = 10
elif age >= 65:
price = 5
```
## 5.4.2 确定列表不是空的
```
requested_toppings = []
#判断列表是不是不为空
if requested_toppings:
```
