On Fri, Sep 3, 2021 at 9:35 AM Guido van Rossum <gu...@python.org> wrote:
> The question is, would anyone ever want to make a distinction between the > two in *real* code? > I expect not. However, finer grained exception may help with debugging and testing. -CHB 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/> > _______________________________________________ > 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/MXVBSNUTLVJVKWIVUK7MSCKM4YDPEL4Y/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- Christopher Barker, PhD (Chris) Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython
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