Python学习笔记第六天

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}