float not understood as numbers.Number

[jordan-schneider]

Please provide more information to help us understand the issue:

• Are you reporting a bug, or opening a feature request? Reporting a bug
• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

import numbers

a: float = 5.0
print(isinstance(a, numbers.Number))  # True

def f(a: float) -> numbers.Number:
    return a  # Incompatible return value type (got "float", expected "Number")

• What is the actual behavior/output?
  Mypy reports the error "Incompatible return value type (got "float", expected "Number")".
• What is the behavior/output you expect?
  I expect mypy to report no errors.
• What are the versions of mypy and Python you are using?
  mypy 0.660
  Python 3.6.8
  Do you see the same issue after installing mypy from Git master?
  Yes.
• What are the mypy flags you are using? (For example --strict-optional)
  None.

I'm slightly unclear if this is really a bug because I don't really understand what numbers is doing but isinstance() returns true, so I would expect the above code to be fine.

Thanks!

[ilevkivskyi]

This a (yet another) duplicate of #3186