On Fri, Sep 3, 2021 at 1:13 PM Guido van Rossum <gu...@python.org> wrote:
> But the text of the error message will explain all you need for debugging > and testing. > debugging, probably yes. But it's a lot easier to check that a particular Exception is raised than to have to check for the Exception and also parse the error message. Honestly, I haven't figured out a use case for this particular example, but I do appreciate finer grained Exceptions in general. -CHB 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 >> > > > -- > --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/> > -- Christopher Barker, PhD (Chris) Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython
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