On Wed, Apr 21, 2021 at 4:44 PM Christopher Barker <python...@gmail.com> wrote: >> You say this like it's a bad thing, but how is this avoidable, even in >> principle? Structural typing lets you check whether Foo is duck-shaped >> -- has appropriate attribute names, etc. But quacking like a duck is >> harder: you also have to implement the Sequence behavioral contract, >> and realistically the only way to know that is if the author of Foo >> tells you. > > > But that's not what duck typing is (at least to me :-) ) For a given > function, I need the passed in object to quack (and yes, I need that quack to > sound like a duck) -- but I usually don't care whether that object waddles > like a duck.
I agree with Christopher here. For duck typing, all we care is that the method(s) we need are implemented in a sensible way. > And this is not uncommon -- I suspect it's very rare for a single function to > use most of the methods of a given ABC (or protocol, or whatever). Also agree, and very often the function cares only about one single method. > And a lot of the standard library works exactly this way. Totally. I found it astonishing that PEP 484 did not allow to correctly annotate LOTS of functions in the standard library, including built-ins people use every day like `sorted()`. Fortunately, that was corrected with PEP 544. > But there is the "culture" of Python -- and it has been very much shifting > toward more typing I disagree because Python is too widespread these days to talk about "the culture". We'll just need to learn to coexist as groups that use the language differently. -- A recent publication (sorry can't find it now -- my google fu is failing me) examined code on PyPi and found a lot of type hints -- many of which were apparently not being used with a static type checker. So why were they there? Maybe you mean this one: "Python 3 types in the wild: a tale of two type systems" Metadata: https://dl.acm.org/doi/10.1145/3426422.3426981 PDF: http://hirzels.com/martin/papers/dls20-python-types.pdf > And I've seen a lot more isinstance(Some_ABC) code lately as well. I believe a lot of that is people coming from statically typed languages and not feeling comfortable with duck typing, while for some other reason not adopting type hints. > From looking at the work of my beginning students, I can tell that they are > seeing examples out there that use more typing, to the point that they think > it's a best practice (or maybe even required?). It is considered best practice in some places. I hope we as a community never adopt it as the canonical way. > Maybe it is -- but if the community is moving that way, we should be honest > about it. Clearly parts of the community are moving that way. The paper I linked shows the use of type hints is still very limited in their sample. >> I'm not even sure that this *is* nominal typing. You could just as >> well argue that "the operation `isinstance(..., Sequence)` returns >> `True`" is just another of the behavioral constraints that are >> required to quack like a sequence. It is not just nominal typing because of the subclass hook. > I'm not sure of the definition of "nominal" typing -- but it absolutely is > NOT duck typing (As Luciano pointed out, Alex Martelli coined the term Goose > Typing for this). Yes. I wish Alex joined this conversation. Cheers, Luciano On Wed, Apr 21, 2021 at 8:28 PM Luciano Ramalho <luci...@ramalho.org> wrote: > > On Wed, Apr 21, 2021 at 4:44 PM Christopher Barker <python...@gmail.com> > wrote: > >> You say this like it's a bad thing, but how is this avoidable, even in > >> principle? Structural typing lets you check whether Foo is duck-shaped > >> -- has appropriate attribute names, etc. But quacking like a duck is > >> harder: you also have to implement the Sequence behavioral contract, > >> and realistically the only way to know that is if the author of Foo > >> tells you. > > > > > > But that's not what duck typing is (at least to me :-) ) For a given > > function, I need the passed in object to quack (and yes, I need that quack > > to sound like a duck) -- but I usually don't care whether that object > > waddles like a duck. > > I agree with Christopher here. For duck typing, all we care is that > the method(s) we need are implemented in a sensible way. > > > And this is not uncommon -- I suspect it's very rare for a single function > > to use most of the methods of a given ABC (or protocol, or whatever). > > Also agree, and very often the function cares only about one single method. > > > And a lot of the standard library works exactly this way. > > Totally. I found it astonishing that PEP 484 did not allow to > correctly annotate LOTS of functions in the standard library, > including built-ins people use every day like `sorted()`. Fortunately, > that was corrected with PEP 544. > > > But there is the "culture" of Python -- and it has been very much shifting > > toward more typing > > I disagree because Python is too widespread these days to talk about > "the culture". We'll just need to learn to coexist as groups that use > the language differently. > > -- A recent publication (sorry can't find it now -- my google fu is > failing me) examined code on PyPi and found a lot of type hints -- > many of which were apparently not being used with a static type > checker. So why were they there? > > Maybe you mean this one: > > "Python 3 types in the wild: a tale of two type systems" > Metadata: > https://dl.acm.org/doi/10.1145/3426422.3426981 > PDF: > http://hirzels.com/martin/papers/dls20-python-types.pdf > > > And I've seen a lot more isinstance(Some_ABC) code lately as well. > > I believe a lot of that is people coming from statically typed > languages and not feeling comfortable with duck typing, while for some > other reason not adopting type hints. > > > From looking at the work of my beginning students, I can tell that they are > > seeing examples out there that use more typing, to the point that they > > think it's a best practice (or maybe even required?). > > It is considered best practice in some places. I hope we as a > community never adopt it as the canonical way. > > > Maybe it is -- but if the community is moving that way, we should be honest > > about it. > > Clearly parts of the community are moving that way. The paper I linked > shows the use of type hints is still very limited in their sample. > > >> I'm not even sure that this *is* nominal typing. You could just as > >> well argue that "the operation `isinstance(..., Sequence)` returns > >> `True`" is just another of the behavioral constraints that are > >> required to quack like a sequence. > > It is not just nominal typing because of the subclass hook. > > > I'm not sure of the definition of "nominal" typing -- but it absolutely is > > NOT duck typing (As Luciano pointed out, Alex Martelli coined the term > > Goose Typing for this). > > Yes. I wish Alex joined this conversation. > > Cheers, > > Luciano > > -- > Luciano Ramalho > | Author of Fluent Python (O'Reilly, 2015) > | http://shop.oreilly.com/product/0636920032519.do > | Technical Principal at ThoughtWorks > | Twitter: @ramalhoorg -- Luciano Ramalho | Author of Fluent Python (O'Reilly, 2015) | http://shop.oreilly.com/product/0636920032519.do | Technical Principal at ThoughtWorks | Twitter: @ramalhoorg _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/SMHPO3TNWLW5C5ZYWXNCRCZB7PXWWDZM/ Code of Conduct: http://python.org/psf/codeofconduct/
