Please provide more information to help us understand the issue:

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

class C:
    def __getattr__(self, name: str) -> 'C':
        ...


def f(v: C) -> None:
    v[0]

• What is the actual behavior/output?
  segfault

• What is the behavior/output you expect?
  not crashing

• What are the versions of mypy and Python you are using?
  python 3.6.7 on Ubuntu 18.04.2 x86_64
  mypy 0.670 installed march 20 2019 via pip

  Do you see the same issue after installing mypy from Git master?
  yes
  0.680+dev.4e0a1583aeb00b248e187054980771f1897a1d31

• What are the mypy flags you are using? (For example --strict-optional)
  none