A dict subclass instance is empty after initialization

August 4, 2023

I try to inherit a dict class, by implementing some logic during the initialization. To do so I add some of the key-value pairs in __init()__ method.

However, after initialization, the instance of my child class is always empty.

import copy
class my_dict(dict):
    def __init__(self, raw_dict):
        self = copy.deepcopy(raw_dict)
        self['bar'] = raw_dict['foo']


original = {'foo' : 'apple'}
alfa = my_dict(original)
print(alfa)

prints empty dict while the expectation would be

[{'foo': 'apple', 'bar': 'apple'}]

How can I achieve the desired behaviour?

>Solution :

You can use the super constructor to do the effect you are looking for:

import copy
class my_dict(dict):
    def __init__(self, raw_dict):
        super().__init__(copy.deepcopy(raw_dict))
        self['bar'] = raw_dict['foo']