list.append() automatically updates dictionary values?-CodePudding

Does anyone know why my dictionary updated automatically even though I didn't use the dict.update() method?

fruits = { "green" : ["kiwi"] }

name = "avocado"    
list_tmp = fruits.get("green")
list_tmp.append(name)

print(fruits)

# output:
 {'green': ['kiwi', 'avocado']}

CodePudding user response：

In Python, both dict and list are mutable. This means that whenever you alter list_tmp, you change fruits.

fruits.get("green") returns not a copy of the list, but the list itself. Then you change the list. The item of the dictionary “points” to an altered list now.

CodePudding user response：

In order to make changes on a copy of your dictionary follow the code below:

import copy


fruits = { "green" : ["kiwi"] }
fruits2=copy.deepcopy(fruits)
name = "avocado"    
list_tmp = fruits2["green"]
list_tmp.append(name)