Internal error in overriding __getitem__ when inheriting from a dict.

[adamjsawicki]

Saw #1269 but believe that's a different matter.

Encountered the following internal error:

Traceback:

$ mypy --show-traceback script.py
script.py:3: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues version: 0.660
Traceback (most recent call last):
  File "/usr/local/bin/mypy", line 10, in <module>
    sys.exit(console_entry())
  File "/usr/local/lib/python3.7/site-packages/mypy/__main__.py", line 7, in console_entry
    main(None)
  File "/usr/local/lib/python3.7/site-packages/mypy/main.py", line 91, in main
    res = build.build(sources, options, None, flush_errors, fscache)
  File "/usr/local/lib/python3.7/site-packages/mypy/build.py", line 157, in build
    result = _build(sources, options, alt_lib_path, flush_errors, fscache)
  File "/usr/local/lib/python3.7/site-packages/mypy/build.py", line 212, in _build
    graph = dispatch(sources, manager)
  File "/usr/local/lib/python3.7/site-packages/mypy/build.py", line 2246, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.7/site-packages/mypy/build.py", line 2544, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/usr/local/lib/python3.7/site-packages/mypy/build.py", line 2659, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/usr/local/lib/python3.7/site-packages/mypy/build.py", line 1803, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 282, in check_first_pass
    self.accept(d)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 393, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/nodes.py", line 851, in accept
    return visitor.visit_class_def(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 1536, in visit_class_def
    self.accept(defn.defs)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 393, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/nodes.py", line 916, in accept
    return visitor.visit_block(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 1700, in visit_block
    self.accept(s)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 393, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/nodes.py", line 614, in accept
    return visitor.visit_func_def(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 704, in visit_func_def
    self._visit_func_def(defn)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 708, in _visit_func_def
    self.check_func_item(defn, name=defn.name())
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 770, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 931, in check_func_def
    self.accept(item.body)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 393, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/nodes.py", line 916, in accept
    return visitor.visit_block(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 1700, in visit_block
    self.accept(s)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 393, in accept
    stmt.accept(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/nodes.py", line 971, in accept
    return visitor.visit_assignment_stmt(self)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 1708, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None, s.new_syntax)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 1763, in check_assignment
    if self.check_compatibility_all_supers(lvalue, lvalue_type, rvalue):
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 1864, in check_compatibility_all_supers
    base_type, base_node = self.lvalue_type_from_base(lvalue_node, base)
  File "/usr/local/lib/python3.7/site-packages/mypy/checker.py", line 1951, in lvalue_type_from_base
    assert self_type is not None, "Internal error: base lookup outside class"
AssertionError: Internal error: base lookup outside class
script.py:3: : note: use --pdb to drop into pdb

Minimal repro:

class Configuration(dict):
    def __init__(self, values: dict):
        self.values: dict = {}

    def __getitem__(self, key: str):
        return self.values[key.lower()]

Realized I don't need to inherit from dict for my desired functionality, but figured I'd post anyway.

[JelleZijlstra]

Confirmed. The crash also happens on latest master and with either the old or the new semantic analyzer.

[ilevkivskyi]

This is not related to __getitem__(), a class with only __init__() causes the same crash:

class Configuration(dict):
    def __init__(self, values: dict):
        self.values: dict = {}

I think this is a duplicate of #5846