Handling of __new__ ?

[rbtcollins]

Note: if you are reporting a wrong signature of a function or a class in
the standard library, then the typeshed tracker is better suited
for this report: https://github.com/python/typeshed/issues

Please provide more information to help us understand the issue:

• Are you reporting a bug, or opening a feature request?

Feature request or bug, one or other :).

• 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.

# 3.5 compatible syntax
_Example= NamedTuple("Example", [("field", str)])

# Customise to permit optional parameters
class Example(_Example):
    def __new__(cls, *, field=None):
        if field is None:
           field = "default"
        return super().__new__(cls, field=field)

Example()

• What is the actual behavior/output?
  error: too few arguments...
• What is the behavior/output you expect?
  no error
• What are the versions of mypy and Python you are using?
  mypy 0.6
  Python 3.5 and 3.6
  Do you see the same issue after installing mypy from Git master?
  Haven't tested
• What are the mypy flags you are using? (For example --strict-optional)
  --ignore-missing-imports

[ilevkivskyi]

If you are no Python 3.6 why aren't you using:

class Example(NamedTuple):
    field: str = "default"

For older Python versions we have #2683 to track.