several custom eq for python classes in context of serialization

Question

Assume I have some complex class structure with some hierarchy, public and private fields.

I need to do some custom serialization for such class. In some test after deserialize I want to compare entities of original object and deserialized one. But since serialization is custom - some fields could differ. For example

class A:
    def __init__(self):
        self.a = 0
        self.b = 1

    def __eq__(self, other_deserialized):
        return self.a == other_deserialized.a

So in context of serialization objects are equal because field 'a' are equal ( that only thing I interested in serialization). But in some other context I wish to compare objects by all fields so I would want to have

class A:
    def __init__(self):
        self.a = 0
        self.b = 1

    def __eq__(self, other):
        return (self.a == other.a) and (self.b == other.b)

So looks like I need to custome equality operator for such purposes. Is there some elegance way to solve this?

Probably I was not clear enough. I meant how to deal with sitiuation, I need two equal operators ( one custom for partly deserialized objects and another for full objects compariosn ) — Anton
– Anton, Commented Jul 6, 2024 at 14:08

Victor Egiazarian · Accepted Answer · 2024-07-06 14:19:42Z

3

I would recommend you to implement just an additional method for your custom comparison. This would be much more clean and scalable approach. Something like this:

class A:
    def __init__(self):
        self.a = 0
        self.b = 1

    def __eq__(self, other: "A") -> bool:
        return (self.a == other.a) and (self.b == other.b)

    def is_equal_by_a(self, other: "A") -> bool:
        """Compare object by 'a' attribute only."""

        return self.a == other.a


first_object = A()
second_object = A()

first_object == second_object  # For common comparison
first_object.is_equal_by_a(other=second_object)  # For comparing by a only

answered Jul 6, 2024 at 14:19

Victor Egiazarian

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2 Comments

Anton Over a year ago

Got it! Then probably would be better to move method "is_equal_by_a" in some other class/file i.e. make some helper function ? To avoid interface complexity of class A

Victor Egiazarian Over a year ago

Depends on your case, but it could be an option, yes)

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