使用if语句操作列表

• Q：检查特殊元素
• A：使用for in 循环

requested_topping = ["mushrooms","green peppers","extra cheese"]

for requested _topping in requested_toppings:
    print("Adding"  + "requested_topping + ",")
print("/nFinshed makeing your pozza!")
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Adding mushrooms.
Adding green peppers.
Adding extra cheese.
finished making your pizza!

#如果披萨店的青椒用完了如何处理
for requested _topping in requested_toppings:
    if requested_topping == "green peppers":
        print("Sorry,we are out of green peppers right now.")
    else:
        pprint("Adding " + requested_topping +".")
print("/nFinished making your  pizza!")
---------------------------------------------------------------------------------------------------------------------------------
Adding mushrooms.
Sorry,we are out of green peppers right now.
Adding extra cheese.

Finshed making your pizza!

• Q：确定列表不是空的
• A：if +列表名 检查是否为空列表

requested_ toppings = []
if requested_ toppings:
    for requested. _topping in requested_ _toppings:
        print("Adding” + requested_ topping +.")
    print("
Finished making your pizza!")
else:
    print("Are you sure you want a plain pizza?")
#在if列表中将列表名用在条件表达式中，python将在列表至少包含一个元素时返回Ture，并在列表为空时返回False。

• Q：使用多个列表
• A：如下

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("/nFinshed making your pozza!")