1. Python的if语句基本语法

• else语句可以省略

age = 12 
if age < 4: 
  price = 0 
elif age < 18: 
  price = 5 
elif age < 65: 
  price = 10
print("Your admission cost is $" + str(price) + ".")

• 支持 5 < age <20
• 支持not in 和 !=判断
• and和or为快速and和快速or。假如or语句的第一个判断返回为True，则不执行第二个判断语句

if 5 < age <20:
  pass

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

car = 'subaru' 
print("Is car == 'subaru'? I predict True.") 
print(car == 'subaru') 
print("\nIs car != 'audi'? I predict False.") 
print(car != 'audi')

• if语句没有变量作用域，也就是if语句下的变量可以在外部直接使用

age = 3
if 5 < age < 18:
    price = 3
else:
    price = 8
print(f"Your admission cost is ${price}.")