On Thu, Sep 1, 2016 at 5:46 PM, Guido van Rossum <gu...@python.org> wrote: > On Thu, Sep 1, 2016 at 6:11 AM, Koos Zevenhoven <k7ho...@gmail.com> wrote: >> While a large amount of Python programmers may not be interested in >> type hinting local variables inside functions, I can see other >> potential benefits in this. > > IOW, PEP 3157 is not dead yet. Indeed. >
PEP 3157? Is that a typo or is there such a thing somewhere? [...] >> Also, when reading code, it may be hard to tell which (instance) >> attributes the class implements. To have these listed in the beginning >> of the class could therefore improve the readability. > > Right. That has been my observation using PEP 484's type comments > extensively for annotating instance variables at the class level. E.g. > much of mypy's own code is written this way, and it really is a huge > help. But > > foo = None # type: List[int] > > while it gives me the info I'm looking for, is not great > notation-wise, and that's why I started thinking about an alternative: > > foo: List[int] > > (in either case, the __init__ contains something like `self.foo = []`). > >> In this light, I'm not sure it's a good idea to allow attribute type >> hints inside methods. > > Those are meant for the coding style where all attributes are > initialized in the method and people just want to add annotations > there. This is already in heavy use in some PEP-484-annotated code > bases I know of, using # type comments, and I think it will be easier > to get people to switch to syntactic annotations if they can > mechanically translate those uses. (In fact we are planning an > automatic translator.) I suppose the translator would be somewhat more complicated if it were to move the type hints to the beginning of the class suite. Anyway, I hope there will at least be a recommendation somewhere (PEP 8?) to not mix the two styles of attribute annotation (beginning of class / in method). The whole readability benefit turns against itself if there are some non-ClassVar variables annotated outside __init__ and then the rest somewhere in __init__ and in whatever initialization helper methods __init__ happens to call. [...] >> Note that we could then also have this: >> >> def NAME >> >> Which would, again for readability (see above), be a way to express >> that "there is an instance variable called X, but no type hint for >> now". I can't think of a *good* way to do this with the keyword-free >> version for people that don't use type hints. >> >> And then there could also be a simple decorator like >> @slotted_attributes that automatically generates "__slots__" from the >> annotations. > > This I like, or something like it. It can be a follow-up design. (I.e. > a separate PEP, once we have experiece with PEP 526.) I think there should be a syntax for this that does not involve type hints, but I can't seem to come up with anything that works with the keyword-free version :(. -- Koos > -- > --Guido van Rossum (python.org/~guido) -- + Koos Zevenhoven + http://twitter.com/k7hoven + _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
