开发笔记:Python(13)_if语句

# if 语句与for循环语句，这个模式在实际编程中经常用
cars = [‘audi‘,‘bmw‘,‘subaru‘,‘toyota‘]
for car in cars:
if car == ‘bmw‘:
print(car.upper())
else:
print(car.title())

# if语句
age =7;
if age>=18:
print("You are old enough to vote!")
# if与else
if age>=18:
print("You are old enough to vote!")
else:
print("Sorry,you are too young to vote.")

# 使用多个elif代码块
age = 12
if age<4:
price = 0
elif age<18:
price = 5
elif age<65:
price=10
else:
price =5
print("Your admission cost is $"+str(price)+".")

‘‘‘else 是一条包罗万象的语句，只要不满足任何if 或elif 中的条件测试，其中的代码就会执行，这可能会引入无效甚至恶意的数据。如果知道最终要测试的条件，应考虑使用
一个elif 代码块来代替else 仅当满足相应的条件时，你的代码才会执行。‘‘‘
# 省略else代码块
age = 98
if age<4:
price = 0
elif age<18:
price = 5
elif age<65:
price=10
elif age>=65:
price =5
print("Your admission cost is $"+str(price)+".")

‘‘‘在这里，我们首先创建了一个空列表，其中不包含任何配料。在处我们进行了简单检查，而不是直接执行for 循环。在if 语句中将列表名用在条件表达式中
时，Python将在列表至少包含一个元素时返回True ，并在列表为空时返回False 。如果requested_toppings 不为空，就运行与前一个示例相同的for 循环；否则，就打印
一条消息，询问顾客是否确实要点不加任何配料的普通比萨‘‘‘
requests =[]
if requests:
for request in requests:
print("Adding "+request+".")
print("
Finished making your pizza")
else:
print("Are you sure you want a plain pizza")

# 多个列表，这种形式的在实际编码中也常见
available_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 available_toppings:
print("Adding "+requested_topping+".")
else:
print("Sorry,we don‘t have "+requested_topping)
print("
Finished making your pizza")