assert user_data == {
        'id': IsPositiveInt,
        'avatar_file': IsStr(regex=r'/[a-z0-9\-]{10}/example\.png'),

> Without dirty-equals, you'd have to compare individual fields and/or modify some fields before comparison ...

Hmm, I'm not convinced. Why not

    assert dirty_check(user_data, {
        'id': IsPositiveInt,
        'avatar_file': IsStr(regex=r'/[a-z0-9\-]{10}/example\.png'),

It would work just as well without abusing the == operator. Doing so seems like a bit of a gimmick (although the actual functionality of the library looks useful).

Edit: Ah, I guess the difference is that dict.__eq__ (and list.__eq__ and so on) recursively tests equality of all child elements. So to support arbitrary nesting I think it really does have to be the equals operator.