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Internal Error when overriding a generic variable in __init__ #5846

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#7235
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Internal Error when overriding a generic variable in __init__#5846
#7235
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crashpriority-0-high

Description

@d-chambers
d-chambers
opened on Oct 27, 2018

This is a bug report.

I created a simple python file called breakmypy.py which has the following contents:

# contents of breakmypy.py
from collections import UserDict

class MyDict(UserDict):
    def __init__(self):
        self.data: dict = {}

When I run mypy breakmypy.py --show-traceback the following output is emitted:

breakmypy.py:14: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues version: 0.630

Traceback (most recent call last):
  File "/home/derrick_chambers/anaconda3/bin/mypy", line 11, in <module>
    sys.exit(console_entry())
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/__main__.py", line 7, in console_entry
    main(None)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/main.py", line 91, in main
    res = type_check_only(sources, bin_dir, options, flush_errors, fscache)  # noqa
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/main.py", line 148, in type_check_only
    fscache=fscache)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/build.py", line 183, in build
    flush_errors, fscache)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/build.py", line 356, in _build
    graph = dispatch(sources, manager)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/build.py", line 2543, in dispatch
    process_graph(graph, manager)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/build.py", line 2840, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/build.py", line 2963, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/build.py", line 2103, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 256, in check_first_pass
    self.accept(d)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 355, in accept
    stmt.accept(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/nodes.py", line 820, in accept
    return visitor.visit_class_def(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 1461, in visit_class_def
    self.accept(defn.defs)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 355, in accept
    stmt.accept(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/nodes.py", line 885, in accept
    return visitor.visit_block(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 1607, in visit_block
    self.accept(s)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 355, in accept
    stmt.accept(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/nodes.py", line 603, in accept
    return visitor.visit_func_def(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 666, in visit_func_def
    self._visit_func_def(defn)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 670, in _visit_func_def
    self.check_func_item(defn, name=defn.name())
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 732, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 898, in check_func_def
    self.accept(item.body)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 355, in accept
    stmt.accept(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/nodes.py", line 885, in accept
    return visitor.visit_block(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 1607, in visit_block
    self.accept(s)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 355, in accept
    stmt.accept(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/nodes.py", line 933, in accept
    return visitor.visit_assignment_stmt(self)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 1614, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None, s.new_syntax)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 1663, in check_assignment
    if self.check_compatibility_all_supers(lvalue, lvalue_type, rvalue):
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 1755, in check_compatibility_all_supers
    base_type, base_node = self.lvalue_type_from_base(lvalue_node, base)
  File "/home/derrick_chambers/anaconda3/lib/python3.7/site-packages/mypy/checker.py", line 1842, in lvalue_type_from_base
    assert self_type is not None, "Internal error: base lookup outside class"
AssertionError: Internal error: base lookup outside class
breakmypy.py:14: : note: use --pdb to drop into pdb

Activity

  1. ilevkivskyi
    added
    crash
    priority-0-high
    on Oct 27, 2018

  2. ilevkivskyi commented on Oct 27, 2018

    @ilevkivskyi
    ilevkivskyi
    on Oct 27, 2018
    Member

    This still crashes on master, here is a bit more self-contained repro:

    from typing import Generic, TypeVar, Any

T = TypeVar('T')

class B(Generic[T]):
    x: T

class C(B):
    def __init__(self) -> None:
        self.x: Any

    It actually crashes in several similar scenarios, the only requirement is that the variable type in a base class is generic, and it is overridden in a method, I wonder how no one found this before.

    This happens in the part of code that I never understood, there is a method called active_self_type(), but it always returns None at method scope.

  3. ilevkivskyi
    changed the title [-]Internal Failure using UserDict subclass[/-] [+]Internal Error when overriding a generic variable in __ini__[/+] on Oct 28, 2018
  4. ilevkivskyi
    changed the title [-]Internal Error when overriding a generic variable in __ini__[/-] [+]Internal Error when overriding a generic variable in __init__[/+] on Nov 2, 2018

  5. ilevkivskyi commented on Dec 8, 2018

    @ilevkivskyi
    ilevkivskyi
    on Dec 8, 2018
    Member

    This crash appeared again in #6033

  6. Levitanus commented on Jan 19, 2019

    @Levitanus
    Levitanus
    on Jan 19, 2019

    in addition
    input_python_file.txt
    traceback.txt

  7. wiml commented on Feb 20, 2019

    @wiml
    wiml
    on Feb 20, 2019

    I just hit this crash in version 0.670 (and 0.660); my minimized case is very similar to the one in ilevkivskyi's comment.

  8. mthuurne commented on Apr 26, 2019

    @mthuurne
    mthuurne
    on Apr 26, 2019
    Contributor

    I hit this error in mypy 0.701, also with a method that overrides the type of a base class member that was generic in the base class.

  9. mthuurne commented on Apr 26, 2019

    @mthuurne
    mthuurne
    on Apr 26, 2019
    Contributor

    I found a workaround:

    from typing import Generic, TypeVar, TYPE_CHECKING

T = TypeVar('T')

class B(Generic[T]):
    x: T

class C(B[int]):

    if TYPE_CHECKING:
        @property
        def x(self) -> str: # type: ignore
            return self.x

reveal_type(C().x)
  10. ilevkivskyi
    closed this as completedin #7235on Jul 18, 2019
  11. ilevkivskyi
    added a commit that references this issue on Jul 18, 2019

    Fix the logic in active self-type calculation for current scope (#7235)

    0b59a10
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