One dictionary changes value while I'm working on another dictionary-CodePudding

I'm struggling with dictionaries

dic1 = {"A":"a","B":"b","C":"c"}
dic2 = dic1
dic2["D"]="d"
print(dic1)

output:

{'A': 'a', 'B': 'b', 'C': 'c', 'D': 'd'}

Could someone explain me why dic1 also appended "D" key with "d" value? And what can I do to avoid this problem? I really want dic1 to not change values

CodePudding user response：

This is happening because you're working with references. This guide is a great explanation of Python references.

To avoid this problem, try the following:

dic1 = {"A":"a","B":"b","C":"c"}
dic2 = dic1.copy()

CodePudding user response：

This is the fundamental property of Python objects. When you naively assign an existed object to a new one, the new one actually points to the first object. With dict2 = dict1, you are actually pointing to the same object. That means every change you make in dict2 will affect the original object. In case you want to copy a dictionary, try dict2 = dict(dict1).