1.条件测试

检验是否相等

///car = 'bmw' car == 'bmw' // True

两个等号是发问，car == 'bmw’可解读为 变量car的值是 bmw 吗？

检验特定值是否在表达式中

检验shengnan这个名字是否在列表中，返回值为True or Flase

//names = ['xiaoming','zhangsan','shengnan'] 'shengnan' in names //True

检验xiaosong 这个用户名是否不在列表中

//names = ['xiaoming','zhangsan','shengnan'] user_name = 'xiaosong' if 'user_name' mot in names: print(user_name.title() + "is not in this list")

2.if语句

如果想执行一个代码块，就使用if-elif-else结构；如果运行多个代码块，就是用一系列独立的if语句。 eg 某家披萨店，顾客添加一种配料就打印一条消息，代码如下

//requested_toppings = ['mushrooms','green peppers','extra cheese'] for requested_topping in requested_toppings: print("Adding" + requested_topping + ".") print("\nFinished making your pizza!")

eg 如果披萨店的青椒用完了怎么写呢？

//requested_toppings = ['mushrooms','green peppers','extra cheese'] for requested_topping in requested_toppings: if requested_topping = 'green peppers': print("Sorry,we are out of green pappers right now") else: print("Adding" + requested_topping + ".") print("\nFinished making your pizza!")

3.确定列表不是空的

eg 制作披萨前先查看顾客点的配料单是否为空，若为空，则向顾客确认是否要点普通披萨；若不为空，则按顾客所点制作。

//requested_toppings = [] if requested_toppings: for requested_topping in requested_toppings: print("Adding" + requested_topping + ".") print("\nFinished making your pizza!") else: print("Are you sure you want a palin pizza?")

使用列表名用在if表达式中，则Python将在至少包含1个元素时返回True。

4.使用多个列表

制作两个列表，一个表包含披萨店供应的配料，另一个是顾客要的配料，检查顾客所点的材料，店内是否有此种配料，代码如下：

//available_toppings = ['mushrooms','olives','green pappers'] requested_toppings = ['mushrooms','olives','french fries'] 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("\nFinished making your pizza!")