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dataclass.__eq__ no longer errors on missing attributes in Python 3.13 #134488

Closed as not planned
@willhcr

Description

@willhcr

Bug report

Bug description:

Description

Equality with self now returns True in 3.13 for dataclasses with deleted attributes. Previously, this would raise an exception.

This may be related to changes discussed in #128294. However, unlike
other reports (#120645, #116647) where something that was True in 3.12 is now False or an Exception,
this issue is the inverse. In 3.13, the equality test silently returns True when previously it would raise.

This class is badly behaved, it should probably still raise an error.

Test Case

import dataclasses


@dataclasses.dataclass
class Test:
    a: int

    def __init__(self):
        self.a = 1

    def del_a(self):
        del self.a


o1 = Test()
o2 = Test()

o1.del_a()
o2.del_a()

print(o1 == o1)  # True (3.13), raises AttributeError (3.12)
print(o1 == o2)  # raises AttributeError (3.13, 3.12)
# AttributeError: 'Test' object has no attribute 'a'

CPython versions tested on:

3.13, 3.12

Operating systems tested on:

Linux

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    3.13bugs and security fixes3.14bugs and security fixes3.15new features, bugs and security fixesstdlibPython modules in the Lib dirtopic-dataclassestype-bugAn unexpected behavior, bug, or error

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