Python Day03

3.复制列表

my_foods = ['pizza', 'falafel', 'carrot cake'] 
friend_foods = my_foods[:]

四、元组

1.元组的定义

元组就是不可变的列表。

dimensions = (200, 50) 
print(dimensions[0]) 
print(dimensions[1])
200
50

元组中的元素不可以被更改。

2.遍历元组中的所有值

dimensions = (200, 50)
for dimension in dimensions: 
    print(dimension)
200
50

3.修改元组变量

dimensions = (200, 50)
print("Original dimensions:")
for dimension in dimensions: 
    print(dimension) 
dimensions = (400, 100)
print("\nModified dimensions:") 
for dimension in dimensions:
    print(dimension)

五、if语句

1.示例

cars = ['audi', 'bmw', 'subaru', 'toyota'] 
for car in cars:  
    if car == 'bmw':      
        print(car.upper())    
    else:       
        print(car.title())

2.条件测试。

python使用语义化的方法，用and表示“和”连接多个判断条件，or表示“或”，in表示“包含”，not in表示“不包含”

1.if-elif-else结构

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

else也可被省略。

3.使用if语句处理列表

1.检查特殊元素

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

2.确定列表不是空的

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 plain pizza?")

3.使用多个列表

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("\nFinished making your pizza!")