A Pylint plugin that checks for a specific implementation of Enum subclasses.
$ pip install pylint_enums # a conventional option $ pipenv install pylint_enums # a more modern option
- Follow instructions to add
pylint_enumsas part of your loaded plugins.
- Option 1 (.pylintrc)
- Use pylint normally, i.e.,
$ pylint [filepath]
- Option 2 (command line option)
$ pylint [filepath] --load-plugins=pylint_enums
- Option 1 (.pylintrc)
What this is:
This is a tiny pylint plugin that adds a checker for Enum subclasses. It warns you when you haven't provided a typed annotation for the
value attribute and when a
__str__ method has not been defined for the Enum when the type annotation isn't part of a finite list of simple types.
__str__ declaration is not enforced for the following types:
Why this is helpful:
Typically, the value of an enum doesn't matter.
from enum import Enum class Foo(Enum): FIRST = 'these' SECOND = 'usually' THIRD = 'don\'t' FOURTH = 'matter'
However, in certain applications and/or use-cases, you actually do care about the value of each enum member. Specifically, you may use them as a
verbose_name or a
pretty_name for displaying to the user, or you may want to assign it a stateful value and use its contents later.
from enum import Enum from typing import NamedTuple class FooMember(NamedTuple): label: str rank: int class Foo(Enum): FIRST = FooMember(label='first', rank=1) SECOND = FooMember(label='second', rank=2) THIRD = FooMember(label='third', rank=3) FOURTH = FooMember(label='fourth', rank=4) def __str__(self) -> str: return self.value.label
As of this writing,
mypy==0.600 is unable to infer the types of the member values. They resolve to
reveal_type(Foo) # 'def (value: Any) -> foo.Foo' reveal_type(Foo.FIRST) # 'foo.Foo' reveal_type(Foo.FIRST.value) # 'Any'
This can be problematic for
mypy users that rely on type hints to maintain their code base. When you write a function that returns
Foo.FIRST.value, our tooling is unable to help us figure out whether this value is a
NamedTuple, or some other value. Ideally, we would add additional type hints to the Enum:
class Foo(Enum): value: FooMember FIRST = FooMember(label='first', rank=1) ...
But alas, this requires developer vigilance to remember to do. If you're maintaining many enums across multiple files, it could be annoying to make sure that they and all future defined Enums are adequately typed.
This pylint plugin will raise errors when
value is not typed and when the value is typed to something complex and the Enum is missing a
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