Traceback when TypeVar variable name doesn't match name given and is used with isinstance

[TDHolmes]

This occurs when the TypeVar name doesn't match AND we do an isinstance check on the argument. It is resolved when either of those are fixed/removed. (see repro code below)

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

• What are the versions of mypy and Python you are using?
  mypy version 0.590
  Python 3.6.5 (default, Apr 11 2018, 15:12:33)

• What are the mypy flags you are using? (For example --strict-optional)
  --ignore-missing-imports --show-traceback

Traceback:

$ mypy ~/Desktop/mypy_repro.py --ignore-missing-imports --show-traceback
/Users/tylerholmes/Desktop/mypy_repro.py:4: error: String argument 1 'Point' to TypeVar(...) does not match variable name 'P'
/Users/tylerholmes/Desktop/mypy_repro.py:4: error: "object" not callable
/Users/tylerholmes/Desktop/mypy_repro.py:7: error: Invalid type "mypy_repro.P"
/Users/tylerholmes/Desktop/mypy_repro.py:8: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues version: 0.590
Traceback (most recent call last):
  File "/usr/local/bin/mypy", line 11, in <module>
    sys.exit(console_entry())
  File "/usr/local/lib/python3.6/site-packages/mypy/__main__.py", line 7, in console_entry
    main(None)
  File "/usr/local/lib/python3.6/site-packages/mypy/main.py", line 85, in main
    type_check_only(sources, bin_dir, options, flush_errors)
  File "/usr/local/lib/python3.6/site-packages/mypy/main.py", line 134, in type_check_only
    flush_errors=flush_errors)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 183, in build
    flush_errors, fscache)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 268, in _build
    graph = dispatch(sources, manager)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 2192, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 2477, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 2605, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/usr/local/lib/python3.6/site-packages/mypy/build.py", line 1843, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 252, in check_first_pass
    self.accept(d)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 351, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.6/site-packages/mypy/nodes.py", line 542, in accept
    return visitor.visit_func_def(self)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 607, in visit_func_def
    self._visit_func_def(defn)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 611, in _visit_func_def
    self.check_func_item(defn, name=defn.name())
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 671, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 834, in check_func_def
    self.accept(item.body)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 351, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.6/site-packages/mypy/nodes.py", line 807, in accept
    return visitor.visit_block(self)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 1430, in visit_block
    self.accept(s)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 351, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.6/site-packages/mypy/nodes.py", line 974, in accept
    return visitor.visit_if_stmt(self)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 2294, in visit_if_stmt
    if_map, else_map = self.find_isinstance_check(e)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 2898, in find_isinstance_check
    return conditional_type_map(expr, vartype, type)
  File "/usr/local/lib/python3.6/site-packages/mypy/checker.py", line 3320, in conditional_type_map
    remaining_type = restrict_subtype_away(current_type, proposed_precise_type)
  File "/usr/local/lib/python3.6/site-packages/mypy/subtypes.py", line 817, in restrict_subtype_away
    new_items = [item for item in t.relevant_items()
  File "/usr/local/lib/python3.6/site-packages/mypy/subtypes.py", line 818, in <listcomp>
    if (not (is_proper_subtype(erase_type(item), erased_s) or
  File "/usr/local/lib/python3.6/site-packages/mypy/erasetype.py", line 25, in erase_type
    return typ.accept(EraseTypeVisitor())
  File "/usr/local/lib/python3.6/site-packages/mypy/types.py", line 194, in accept
    return visitor.visit_unbound_type(self)
  File "/usr/local/lib/python3.6/site-packages/mypy/erasetype.py", line 31, in visit_unbound_type
    assert False, 'Not supported'
AssertionError: Not supported
/Users/tylerholmes/Desktop/mypy_repro.py:8: : note: use --pdb to drop into pdb

minimal code to reproduce:

from numbers import Real
from typing import Optional, Tuple, TypeVar, Union

P = TypeVar('Point', bound='Point')


def repro_func(name: str, value: Optional[Union[Real, P]]) -> Tuple[str, Real]:
    if isinstance(value, str):
        value = value[name]
    return name, value


repro_func("hi", None)

[TDHolmes]

And we can't really rename the variable to Point because that collides with the class name Point that exists in this file.

[ilevkivskyi]

The crash is fixed by #5258
Instead mypy gives a bunch of errors:

tstub.py:4: error: String argument 1 'Point' to TypeVar(...) does not match variable name 'P'
tstub.py:4: error: "object" not callable
tstub.py:7: error: Invalid type "tstub.P"
tstub.py:9: error: Invalid index type "str" for "str"; expected type "Union[int, slice]"
tstub.py:10: error: Incompatible return value type (got "Tuple[str, Union[Real, str, None]]", expected "Tuple[str, Real]")

Some of those are reasonable, but "object not callable" is clearly bogus. This is related to have special typing constructs are defined in typeshed. I will open an issue there instead.