[Python-ideas] Comparable exceptions

[Guido van Rossum]

Actually, they don't have a __hash__ either -- they just inherit the
default __hash__ from object, just as they inherit __eq__ from object (and
both just use the address of the object). I can see many concerns with
trying to define __eq__ for exceptions in general -- often there are a
variety of fields, not all of which perhaps should be considered when
comparing, and then there are user-defined exceptions which may have other
attributes. I don't know what your use case was, but if, as you say, the
exceptions you care about already have `args` attributes, maybe you should
just compare that (and the type).

On Tue, Feb 24, 2015 at 3:43 PM, Ionel Cristian Mărieș <contact at ionelmc.ro>
wrote:

> Hey everyone,
>
> I was writing a test the other day and I wanted to assert that some
> function raises some exception, but with some exact value. Turns out you
> cannot compare OSError("foobar") to OSError("foobar") as it doesn't have
> any __eq__. (it's the same for all exceptions?)
>
> I think exceptions are great candidates to have an __eq__ method - they
> already have a __hash__ (that's computed from the contained values) and
> they are already containers in a way (they all have the `args` attribute).
>
> Comparing exceptions in a test assertion seems like a good usecase for
> this.
>
> Thanks,
> -- Ionel Cristian Mărieș, blog.ionelmc.ro
>
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-- 
--Guido van Rossum (python.org/~guido)
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