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 > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/3CLXFC52JIBCFXMXRFA5I6F4RDU5ZYP3/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --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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