[Python-Dev] Is static typing still optional?

[Chris Barker]

On Mon, Dec 18, 2017 at 11:49 PM, Eric V. Smith <eric at trueblade.com> wrote:

> I also don't think it's surprising that you can put misleading information
> (including non-types) in type annotations. All of the documentation and
> discussions are quite clear that type information is ignored at runtime.
>

Sure -- but that's documentation of type annotations -- someone
uninterested in typing, or completely unaware of it, will not be reading
those docs.


> Data Classes is also not the first use of type annotations in the stdlib:
> https://docs.python.org/3/library/typing.html#typing.NamedTuple


That's in the typing package, yes? collections.namedtuple is unchanged. So
yes, obviously the entire typing package is about typing. This is something
that has nothing to do with typing, but does use the typing syntax. It
really is different.

I haven't started teaching typing to newbies yet -- but I imagine I will
have to some day -- and when I do, it will be in the context of: here is an
optional feature that you can use along with a static type checker. And I
can make it clear that the annotations only apply to the static type
checker, and not run-time behavior.

But using type annotations for something other than providing information
to a static type checker, in an stdlib module, changes that introduction.
And people don't read all the docs -- they read to the first example of how
to use it, and away they go. And if that example is something like:

@dataclass
class C:
    a: int
    b: float = 0.0

There WILL be confusion.

Paul Moore wrote:

> Also, the fact that no-one raised this issue during the whole time the
> PEP was being discussed (at least as far as I recollect) and that
> Guido (who of all of us should be most aware of what is and isn't
> acceptable use of annotations in the stdlib) approved the PEP,
> suggests to me that this isn't that big a deal.


That suggests to me that the people involved in discussing the PEP may not
be representative of the bulk of Python users. There are a number of us
that are uncomfortable with static typing in general, and the python-dev
community has been criticised for doing too much, moving too fast, and
complicating the language unnecessarily.

The PEP's been accepted, so let's move forward, but please be aware of
these issues with the documentation and examples.

I'll try to contribute to that discussion as well.

-CHB



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Christopher Barker, Ph.D.
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