On Sun, Jul 26, 2020 at 11:01 PM Ethan Furman <et...@stoneleaf.us> wrote:
> On 7/26/20 10:31 AM, Henry Lin wrote: > > > You're right, declaring `__eq__` for the class we want to compare would > > solve this issue. However, we have the tradeoff that > > > > * All classes need to implement the `__eq__` method to compare two > > instances; > > I usually implement __eq__ sooner or later anyway -- even if just for > testing. > > > * Any class implementing the `__eq__` operator is no longer hashable > > One just needs to define a __hash__ method that behaves properly. > This is quite a significant change in behaviour which may break compatibility. Equality and hashing based only on identity can be quite a useful property which I often rely on. There's another reason people might find this useful - if the objects have differing attributes, the assertion can show exactly which ones, instead of just saying that the objects are not equal. Even if all the involved classes implement a matching repr, which is yet more work, the reprs will likely be on a single line and the diff will be difficult to read.
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