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/
