每日一句：差错发生在细节，成功取决于系统。

if语句处理列表

requested_toppings=[\'mushrooms\',\'gress peppers\',\'extra cheese\']
for requested_topping in requested_toppings:
    print("adding"+requested_topping+\'.\')
print("\nFinished making your pizza!")
addingmushrooms.
addinggress peppers.
addingextra cheese.

Finished making your pizza!
requested_toppings=[\'mushrooms\',\'gress peppers\',\'extra cheese\']
for requested_topping in requested_toppings:
    if requested_topping==\'gress peppers\':
        print("Sorry,we are out of green peppers right now")
    else:
        print("adding "+requested_topping+\'.\')
print("\nFinished making your pizza!")
# 遍历列表，当requested_topping等于gress peppers时，打印else语句，反之打印if语句
 
adding mushrooms.
Sorry,we are out of green peppers right now
adding extra cheese.

Finished making your pizza!
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?")
# 当列表为空时，for循环无法执行，执行了else
Are you sure you want a plain pizza?
avaiblable_toppings=[\'mushrooms\',\'olives\',\'gress peppers\',\'pepperoni\',\'pineapple\',\'extra cheese\']
requested_toppings=[\'mushrooms\',\'french fries\',\'extra cheese\']
for requested_topping in requested_toppings:
    if requested_topping in avaiblable_toppings:
        print("adding"+requested_topping+\'.\')
    else:
        print("Sorry,we don\'t have"+requested_topping+".")
print("\nFinished making your pizza!")
# 遍历列表requested_toppings，当其中的元素不存在在列表avaiblable_toppings中，则执行else语句，反之执行if语句
addingmushrooms.
Sorry,we don\'t havefrench fries.
addingextra cheese.

Finished making your pizza!

字典

字典由{ }包起来
alien_0={\'color\':\'green\',\'point\':5}
print(alien_0[\'color\'])
print(alien_0[\'point\'])
# \'color\':\'green\'组成了一个键值对
# \'color\'代表了键，\'green\'代表值，两者一一对应
green
5
alien_0={\'color\':\'green\',\'point\':5}
print(alien_0[\'color\'])
# 通过访问字典的键来获取字典的值
green

添加键值对

alien_0={\'color\':\'green\',\'point\':5}
print(alien_0)
alien_0[\'x_position\']=0
alien_0[\'y_position\']=25
print(alien_0)
# 字典[]=x 可以添加键值对
{\'color\': \'green\', \'point\': 5}
{\'color\': \'green\', \'point\': 5, \'x_position\': 0, \'y_position\': 25}
alien_1={}
alien_1[\'color\']=\'green\'
alien_1[\'point\']=5
print(alien_1)
{\'color\': \'green\', \'point\': 5}

修改键值对

alien_0={\'color\':\'green\'}
print(alien_0)
alien_0[\'color\']=\'bule\'
print(alien_0)
# 通过对键的重新赋值来修改值
{\'color\': \'green\'}
{\'color\': \'bule\'}

删除键值对

alien_2={\'color\':\'green\',\'point\':5}
print(alien_2)
del alien_2[\'color\']
print(alien_2)
# del 键  删除键值对  删除后键值对将永远消失
{\'color\': \'green\', \'point\': 5}
{\'point\': 5}

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