The question is, would anyone ever want to make a distinction between the
two in *real* code? I find it unlikely that someone would write
try:
sum(x, y, z)
except TypeError:
...
If you bury the sum() call deep inside other code, I'd say your try/except
net is too wide.
On Fri, Sep 3, 2021 at 4:24 AM Oscar Benjamin <oscar.j.benja...@gmail.com>
wrote:
> On Fri, 3 Sept 2021 at 08:10, Serhiy Storchaka <storch...@gmail.com>
> wrote:
> >
> > There are two different kinds of TypeError: if the end user passes an
> > instance of wrong type and if the author of the library makes an error
> > in implementation of some protocols.
> >
> > For example, len(obj) raises TypeError in two cases: if obj does not
> > have __len__ (user error) and if obj.returns non-integer (implementation
> > error). for x in obj raises TypeError if obj does not have __iter__
> > (user error) and if iter(obj) does not have __next__ (implementation
> error).
> >
> > User errors can be fixed on user side, implementation errors can only be
> > fixed by the author of the class. Even if the user and the author is the
> > same person, these errors point to different places of code.
> >
> > Would it be worth to add a special TypeError subclass for implementation
> > errors to distinguish them from user errors? How to name it
> > (ImplementationError, ProtocolError, etc)?
>
> I think that it would be good to make TypeError more fine-grained.
> Another example is:
>
> >>> sum(1, 2, 3)
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> TypeError: sum() takes at most 2 arguments (3 given)
>
> There can be reasons in library code to catch TypeError that might
> arise from bad user input but in those situations you would usually
> not want to catch this TypeError. The error from calling a function
> with the wrong number of arguments would usually mean a bug in the
> library code which should not be caught. Conversely if the user input
> is a callable and you do want to catch the error resulting from it
> being called with the wrong number of arguments then catching
> TypeError is too broad again. Something like BadArgumentsError would
> be better.
>
> --
> Oscar
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--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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