[Python-ideas] Proposal: Use mypy syntax for function annotations

[Stephen J. Turnbull]

Andrew Barnert writes:
 > On Thursday, August 14, 2014 10:46 PM, Stephen J. Turnbull <stephen at xemacs.org> wrote:

 > > I think it's reasonable to assume that Ms. U. S. Author didn't think
 > > about the implications of tuples or dictionary views or iterators or
 > > whatever.  I personally think a warning here is a *good* thing: if
 > > Ms. Author didn't intend those usages, why should she have to check
 > > them?
 > 
 > You're forgetting that linting is not the only purpose of static
 > type annotations in this proposal.

Hardly.

 > But if, say, your IDE doesn't suggest a function that it could
 > have, you may never notice the problem, and just find the library
 > to be less fun to use than you expected.

But who decides it *should* be perfectly valid code?  *Somebody* has
to check that, and if code is used naively in a case where it
shouldn't be (cf the "why doesn't sum() handle iter_of_str" thread!),
the user is screwed again.

Have you never written code that was perfectly sound for your purpose,
but could be used in other contexts according to ducktyping?  Are you
*sure* that it is valid in those other contexts?  (Think sum vs.
math.fsum -- accuracy matters.)

Of course it's a matter of balance, and *maybe* it tips more in the
direction of "default to the most general type where the code will run
without crashing or raising".  I'm just saying it's not obvious to me
that it's such a bad thing that one-off piece of junk libraries may
not be as re-abusable if you use a type checker as they are when you
don't.