False positive "Statement is unreachable" when variable is untyped

[dpinol]

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

• Please insert below the code you are checking with mypy,

throw = None
for i in range(0, 2):
    if i == 1:
        if throw is None:
            raise Exception(2)
        print("I reached")
    throw = True

• What is the actual behavior/output?

organization/task/kk.py:6: error: Statement is unreachable  [misc]

• What is the behavior/output you expect?
  No error, since line 6 is reached when executing the code

• What are the versions of mypy and Python you are using?
  mypy 0.761 and python 3.7.5.
  Also fails with mypy from Git master?

• What are the mypy flags you are using? (For example --strict-optional)
  --warn-unreachable

Mypy does not cause false positive when typing the flag "throw"

from typing import Optional

throw: Optional[bool] = None
for i in range(0, 2):
    if i == 1:
        if throw is None:
            raise Exception(2)
        print("I reached")
    throw = True

[Michael0x2a]

Yeah, this is a pretty annoying limitation -- thanks for the report!

This is currently being tracked in #5423; closing this as a dupe.