列表的拷贝

将一个列表的值复制到另一个列表，如将my_foods拷贝到friend_foods，需要使用如下的程序，才可分别对这两个列表的值进行修改，两个列表的值可以不同

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

friend_foods = my_foods[:]   #也可使用   friend_foods = my_foods.copy()

my_foods.append('cannoli')

friend_foods.append('ice cream')

print("My favorite foods are:")

print(my_foods)

print(" My friend's favorite foods are:")

print(friend_foods)

输出

My favorite foods are:

['pizza', 'falafel', 'carrot cake', 'cannoli']

My friend's favorite foods are:

['pizza', 'falafel', 'carrot cake', 'ice cream']

 

 

如果使用

friend_foods = my_foods

my_foods.append('cannoli')

friend_foods.append('ice cream')

print("My favorite foods are:")

print(my_foods)

print(" My friend's favorite foods are:")

print(friend_foods)

输出

My favorite foods are:

['pizza', 'falafel', 'carrot cake', 'cannoli', 'ice cream']

My friend's favorite foods are:

['pizza', 'falafel', 'carrot cake', 'cannoli', 'ice cream']

两个列表的值始终相同

 

 

参考4.4.3节