Reordered file extensions for improved validation

[ksg]

django.core.validators.FileExtensionValidator had an __eq__ method to compare the validator class. However, comparing arrays is not accurate when the order of elements in the arrays is different.

def __eq__(self, other):
    return (
        isinstance(other, self.__class__)
        and sorted(self.allowed_extensions) == sorted(other.allowed_extensions)
        and self.message == other.message
        and self.code == other.code
    )

This test case failed:

self.assertEqual(
    FileExtensionValidator(["jpg", "png", "txt"]),
    FileExtensionValidator(["txt", "jpg", "png"]),
)

So I suggest comparing two extension arrays after sorting them.

[ksg]

PR: ​https://github.com/django/django/pull/17398

[Tim Graham]

I'd think that validators that behave identically should be considered equal. Did you run into a real-world bug with the current behavior?