packages: make hash() consistent and incl features

[abn]

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[radoering]

Just a quick thought when deciding what to put into the hash for each class. In my understanding, it's not required to consider each attribute in the hash even if it is considered for equality. E.g., consider the following slightly exaggerated example:

class A:
    def __init__(self, a):
        self.a = a

    def __hash__(self):
        return 0

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

    def __repr__(self):
        return f'A({self.a})'


s = {A(0), A(1), A(2)}
print(s)

Output: {A(0), A(1), A(2)}

It might be inperformant, but it seems to be valid even though every instance has the same hash.

Thus, I tend to say we have to decide for each attribute:

• relevant for equality? if yes -> use in __eq__
• if used in __eq__, also immutable? if yes -> use in __hash__

In other words, two (simplified) rules that must not be broken:

• attributes used in __hash__ must be used in __eq__
• attributes used in __hash__ must be immutable

[abn]

Split out the attribute change to #375

Resolved by myself. ;)

[sonarcloud]

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[abn]

Changes look good to me. Someone else might need to approve.