8000 internal error using Enum and __new__ · Issue #1081 · python/mypy · GitHub
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bcdarwin opened this issue Dec 17, 2015 · 4 comments
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internal error using Enum and __new__ #1081

bcdarwin opened this issue Dec 17, 2015 · 4 comments
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bug mypy got something wrong

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@bcdarwin
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Making a list of types looks weird, but this was originally used to construct a typing.NamedTuple.

import typing
from typing import Tuple, Callable, Any, List
from enum import Enum

class MyEnum(Enum):
    def __new__(cls): pass

def F(fields: List[Callable[[Any], Any]]): pass

class SomeEnum(MyEnum):
    x = 1

F([SomeEnum])

produces:

Traceback (most recent call last):
  ...
  File "/home/bdarwin/.local/lib/python3.5/site-packages/mypy/types.py", line 346, in accept
    return visitor.visit_callable_type(self)
  File "/home/bdarwin/.local/lib/python3.5/site-packages/mypy/constraints.py", line 231, in visit_callable_type
    template.arg_types[i], cactual.arg_types[i],
IndexError: list index out of range

*** INTERNAL ERROR ***

foo.py:13: error: Internal error -- please report a bug at https://github.com/JukkaL/mypy/issues
The program exited via sys.exit(). Exit status: 1
@bcdarwin bcdarwin changed the title internal error using Enum, NamedTuple internal error using Enum and __new__ Dec 17, 2015
@gvanrossum
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gvanrossum commented Dec 17, 2015 via email

@JukkaL JukkaL added the bug mypy got something wrong label Dec 18, 2015
@gvanrossum
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I've removed a few red herrings from the repro; here's the smallest one I could find:

from typing import Any, Callable, List
def f(fields: List[Callable[[Any], Any]]): pass
class C: pass
f([C])

Some things I tried that went too far:

  • The argument type for f must be a List type
  • The Callable type must have an argument

The class's __init__ signature (here inherited from object) must not match the Callable given.

@gvanrossum
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I think I've got a fix -- let me know if that solves your real-world case (I've already verified it solves the repro given here).

@bcdarwin
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Yeah, that fixes it. Thanks!

@JukkaL JukkaL closed this as completed in 02e88c4 Dec 29, 2015
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