CODEWITHSUNDEEP
pythonpython-dataclasses
Joost Döbken
Joost Döbken

Reputation: 4035

Extend immutable (frozen) dataclasses

I found the use of a frozen dataclass the most clean solution to make Python objects immutable. The implementation is really simple adding a single class decorator:

from dataclasses import dataclass

@dataclass(frozen=True)
class Immutable:
    attr1: int
    attr2: int

Now I want to extend the Immutable class by introducing a new attribute attr3:

class MyImmutableChild(Immutable):
    attr3: int

But, the behavior is not as expected:

>>> immutable_obj = MyImmutableChild(attr1=1, attr2=3, attr3=5)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-2b6c18366721> in <module>
----> 1 immutable_obj = MyImmutableChild(attr1=1, attr2=3, attr3=5)

TypeError: __init__() got an unexpected keyword argument 'attr3'

Upvotes: 2

Views: 367

Answers (1)

Joost D&#246;bken
Joost D&#246;bken

Reputation: 4035

Ah, this is simply solved by adding another @dataclass(frozen=True) decorator to the child class

Upvotes: 2

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