Internal error on overloaded __getitem__

[mgeisler]

I was testing how to make a generic Sequence with an overloaded __getitem__ and had these input files:

# test.py
import overload
c = overload.Container
c[10] = 20

# overload.py
class Container:
    def __getitem__(self, key):
        pass

# overload.pyi
from typing import TypeVar, Generic, Sequence, overload
T = TypeVar('T')

class Container(Generic[T], Sequence[T]):

    @overload
    def __getitem__(self, key: int) -> T: ...

    @overload
    def __getitem__(self, key: slice) -> Sequence[T]: ...

Running mypy test.py produces

Traceback (most recent call last):
  File "/home/mg/.virtualenvs/mypy/bin/mypy", line 6, in <module>
    exec(compile(open(__file__).read(), __file__, 'exec'))
  File "/home/mg/src/mypy/scripts/mypy", line 6, in <module>
    main(__file__)
  File "/home/mg/src/mypy/mypy/main.py", line 50, in main
    type_check_only(sources, bin_dir, options)
  File "/home/mg/src/mypy/mypy/main.py", line 94, in type_check_only
    python_path=options.python_path)
  File "/home/mg/src/mypy/mypy/build.py", line 210, in build
    result = manager.process(initial_states)
  File "/home/mg/src/mypy/mypy/build.py", line 425, in process
    next.process()
  File "/home/mg/src/mypy/mypy/build.py", line 930, in process
    self.type_checker().visit_file(self.tree, self.tree.path)
  File "/home/mg/src/mypy/mypy/checker.py", line 409, in visit_file
    self.accept(d)
  File "/home/mg/src/mypy/mypy/checker.py", line 450, in accept
    typ = node.accept(self)
  File "/home/mg/src/mypy/mypy/nodes.py", line 564, in accept
    return visitor.visit_assignment_stmt(self)
  File "/home/mg/src/mypy/mypy/checker.py", line 1122, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None)
  File "/home/mg/src/mypy/mypy/checker.py", line 1167, in check_assignment
    self.check_indexed_assignment(index_lvalue, rvalue, rvalue)
  File "/home/mg/src/mypy/mypy/checker.py", line 1499, in check_indexed_assignment
    self.try_infer_partial_type_from_indexed_assignment(lvalue, rvalue)
  File "/home/mg/src/mypy/mypy/checker.py", line 1513, in try_infer_partial_type_from_indexed_assignment
    if var is not None and isinstance(var.type, PartialType):
AttributeError: 'TypeInfo' object has no attribute 'type'

*** INTERNAL ERROR ***

test.py:4: error: Internal error

---

Testing some more, I see the same error when I remove the overloaded __getitem__ method and test with

# overload.pyi
from typing import TypeVar, Generic, Sequence
T = TypeVar('T')


class Container(Generic[T], Sequence[T]):
    pass

This is with mypy 0ec0cb4.

[JukkaL]

Thanks for reporting the bug! I was able to reproduce it using the latest master.

[gvanrossum]

One-file repro:

from typing import TypeVar, Generic, Sequence

T = TypeVar('T')

class Container(Sequence[T]):
    pass

Container[10] = 20