AssertionError: Var(forward) in check_method_override_for_base_with_name

[zasdfgbnm]

This happens when I replace the with_metaclass from six with metaclass=.

I am sorry that I don't have a minimum repro(but please let me know if you need help on reproducing with the method below).

To reproduce, clone pytorch/pytorch#42199 and run

mypy torch/jit/quantized.py --show-traceback

I believe the error is cause by this line:
https://github.com/pytorch/pytorch/pull/42199/files#diff-e8275ad00ce28cc930d6c736043ad876R264

And you will see:

torch/jit/quantized.py:171: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.790+dev.3b57105ef75d8f8f479e1617c035320b80b1bcfa.dirty
torch/jit/quantized.py:171: : note: use --pdb to drop into pdb
Var(forward) <class 'mypy.nodes.Var'>
Traceback (most recent call last):
  File "/home/gaoxiang/.local/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/__main__.py", line 8, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/main.py", line 90, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/build.py", line 180, in build
    result = _build(
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/build.py", line 254, in _build
    graph = dispatch(sources, manager, stdout)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/build.py", line 2630, in dispatch
    process_graph(graph, manager)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/build.py", line 2953, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/build.py", line 3060, in process_stale_scc
    if not graph[id].type_check_second_pass():
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/build.py", line 2128, in type_check_second_pass
    return self.type_checker().check_second_pass()
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/checker.py", line 344, in check_second_pass
    self.check_partial(node)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/checker.py", line 356, in check_partial
    self.accept(node)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/checker.py", line 401, in accept
    stmt.accept(self)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/nodes.py", line 767, in accept
    return visitor.visit_decorator(self)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/checker.py", line 3594, in visit_decorator
    self.check_method_override(e)
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/checker.py", line 1421, in check_method_override
    if self.check_method_or_accessor_override_for_base(defn, base):
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/checker.py", line 1449, in check_method_or_accessor_override_for_base
    if self.check_method_override_for_base_with_name(defn, name, base):
  File "/home/gaoxiang/.local/lib/python3.8/site-packages/mypy/checker.py", line 1511, in check_method_override_for_base_with_name
    assert False, str(base_attr.node)
AssertionError: Var(forward)

[ilevkivskyi]

Most likely this is a duplicate of #5425