[Python-Dev] What's missing in PEP-484 (Type hints)

[Florian Bruhin]

* Dima Tisnek <dimaqq at gmail.com> [2015-04-30 13:41:53 +0200]:
> # lambda
> Not mentioned in the PEP, omitted for convenience or is there a rationale?
> f = lambda x: None if x is None else str(x ** 2)
> Current syntax seems to preclude annotation of `x` due to colon.
> Current syntax sort of allows lamba return type annotation, but it's
> easy to confuse with `f`.

Not sure if you'd really want to stuff type annotations into a
lambda... at that point you'd IMHO be better off by using a real
function.

> # local variables
> Not mentioned in the PEP
> Non-trivial code could really use these.
> 
> 
> # global variables
> Not mentioned in the PEP
> Module-level globals are part of API, annotation is welcome.
> What is the syntax?
> 
> 
> # comprehensions
> [3 * x.data for x in foo if "bar" in x.type]
> Arguable, perhaps annotation is only needed on `foo` here, but then
> how complex comprehensions, e.g. below, the intermediate comprehension
> could use an annotation
> [xx foj y in [...] if ...]
> 
> 
> # class attributes
> s = socket.socket(...)
> s.type, s.family, s.proto  # int
> s.fileno  # callable
> If annotations are only available for methods, it will lead to
> Java-style explicit getters and setters.
> Python language and data model prefers properties instead, thus
> annotations are needed on attributes.
> 
> 
> # plain data
> user1 = dict(id=123,  # always int
>     name="uuu",  # always str
>     ...)  # other fields possible
> smth = [42, "xx", ...]
> (why not namedtuple? b/c extensible, mutable)
> At least one PHP IDE allows to annotate PDO.
> Perhaps it's just bad taste in Python? Or is there a valid use-case?

Most (all?) of this is actually mentioned in the PEP:
https://www.python.org/dev/peps/pep-0484/#type-comments

Florian

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