Internal error in check_method_override_for_base_with_name

[jabdoa2]

We get an internal error in mypy 0.501 (latest from pip):

myfile.py:270: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues
Traceback (most recent call last):
  File "/usr/lib/python3.4/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.4/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.4/dist-packages/mypy/__main__.py", line 5, in <module>
    main(None)
  File "/usr/local/lib/python3.4/dist-packages/mypy/main.py", line 42, in main
    res = type_check_only(sources, bin_dir, options)
  File "/usr/local/lib/python3.4/dist-packages/mypy/main.py", line 86, in type_check_only
    options=options)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 183, in build
    dispatch(sources, manager)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1531, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1768, in process_graph
    process_stale_scc(graph, scc)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1847, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1453, in type_check_first_pass
    self.type_checker.check_first_pass()
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 167, in check_first_pass
    self.accept(d)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 233, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 717, in accept
    return visitor.visit_class_def(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 970, in visit_class_def
    self.accept(defn.defs)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 233, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 778, in accept
    return visitor.visit_block(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 1063, in visit_block
    self.accept(s)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 233, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 601, in accept
    return visitor.visit_decorator(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 2052, in visit_decorator
    e.func.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 536, in accept
    return visitor.visit_func_def(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 425, in visit_func_def
    self.check_method_override(defn)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 836, in check_method_override
    self.check_method_or_accessor_override_for_base(defn, base)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 846, in check_method_or_accessor_override_for_base
    self.check_method_override_for_base_with_name(defn, name, base)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 874, in check_method_override_for_base_with_name
    assert False, str(base_attr.node)
AssertionError: Var(config)

Code at the reported line:

    @property
    def config(self) -> Dict[str, Any]:
        """Return the merged config."""
        config = copy.deepcopy(self._driver.config)
        for name, item in self._config_overwrite.items():
            if item is not None:
                config[name] = item

        return config

[JelleZijlstra]

Which line is line 270?

[jabdoa2]

The def line. Removing the return type does not help here.

[JelleZijlstra]

Looks like this is in a branch where a base class defines the same name, but the type of the attribute on the base class is None. Not sure when that would happen.

Can you provide a small test case that reproduces the error? You'd probably need the base class of the class that triggers the error.

[jabdoa2]

The baseclass defines config as property. This might trigger the error. Can try to write a test case tomorrow

[JelleZijlstra]

Thanks! I tried a couple of variations on that but couldn't reproduce.

[jabdoa2]

Minimal "working" example:

from typing import Any, Dict

class A():

    def __init__(self) -> None:
        self.config = dict()    # no annotation here


class B(A):

    @property
    def config(self) -> Dict[str, Any]:
        return {"a": 7}

Results in this stack trace:

$ python3 -m mypy --show-traceback test.py 
test.py:7: error: Need type annotation for variable
test.py:12: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues
Traceback (most recent call last):
  File "/usr/lib/python3.4/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.4/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.4/dist-packages/mypy/__main__.py", line 5, in <module>
    main(None)
  File "/usr/local/lib/python3.4/dist-packages/mypy/main.py", line 42, in main
    res = type_check_only(sources, bin_dir, options)
  File "/usr/local/lib/python3.4/dist-packages/mypy/main.py", line 86, in type_check_only
    options=options)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 183, in build
    dispatch(sources, manager)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1531, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1768, in process_graph
    process_stale_scc(graph, scc)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1847, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 1453, in type_check_first_pass
    self.type_checker.check_first_pass()
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 167, in check_first_pass
    self.accept(d)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 233, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 717, in accept
    return visitor.visit_class_def(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 970, in visit_class_def
    self.accept(defn.defs)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 233, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 778, in accept
    return visitor.visit_block(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 1063, in visit_block
    self.accept(s)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 233, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 601, in accept
    return visitor.visit_decorator(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 2052, in visit_decorator
    e.func.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 536, in accept
    return visitor.visit_func_def(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 425, in visit_func_def
    self.check_method_override(defn)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 836, in check_method_override
    self.check_method_or_accessor_override_for_base(defn, base)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 846, in check_method_or_accessor_override_for_base
    self.check_method_override_for_base_with_name(defn, name, base)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 874, in check_method_override_for_base_with_name
    assert False, str(base_attr.node)
AssertionError: Var(config)
test.py:12: note: use --pdb to drop into pdb

Indeed when I fix the first error test.py:7: error: Need type annotation for variable this turns into this:

$ python3 -m mypy --show-traceback test.py 
test.py:13: error: Signature of "config" incompatible with supertype "A"

Which I would argue should not be an error because the getter returns exactly the same type:

from typing import Any, Dict


class A():

    def __init__(self) -> None:
        self.config = dict()    # type: Dict[str, Any]


class B(A):

    @property
    def config(self) -> Dict[str, Any]:
        return {"a": 7}

But that might be another issue