References to names before they're bound should generate an error (UnboundLocalError)

[spkersten]

This code raises an error when executed but passes type checking:

def f(x: A): pass

y = A()

class A: pass

[spkersten]

I'm working on a solution for this issue in my 'scope' branch.

[JukkaL]

Yup, mypy is currently too lenient, and catching these errors would be useful.

This should still be fine and we shouldn't complain about this:

def f(x: 'A'):
    y = A()

class A: pass

[carljm]

In Python 3.7, with from __future__ import annotations, the original example here is fine at runtime and should not raise an error in mypy either. See https://www.python.org/dev/peps/pep-0563/

Given that from __future__ import annotations is supposed to become the default behavior over time, perhaps implementing this form of strictness is not a high priority.

[JukkaL]

This is confusing for new users and they might not know about from __future__ import annotations so it would still be nice to generate better error messages.