12.03.21 23:48, Ethan Furman пише:
> A question that comes up quite a bit on Stackoverflow is how to test to
> see if a value will result in an Enum member, preferably without having
> to go through the whole try/except machinery.
>
> A couple versions ago one could use a containment check:
>
> if 1 in Color:
>
> but than was removed as Enums are considered containers of members, not
> containers of the member values. It was also possible to define one's
> own `_missing_` method and have it return None or the value passed in,
> but that has also been locked down to either return a member or raise an
> exception.
>
> At this point I see three options:
>
> 1) add a `get(value, default=None)` to EnumMeta (similar to `dict.get()`
>
> 2) add a recipe to the docs
>
> 3) do nothing
>
> Thoughts?
The Enum class is already too overloaded. I sometimes think about adding
SimpleEnum class with minimal simple functionality which would allow to
use enums in more modules sensitive to import time.
As for solving your problem, try/except looks the best solution to me.
try:
Color(1)
except ValueError:
... # invalid color
else:
... # valid color
If you don't like try/except, the second best solution is to add a
module level helper in the enum module:
def find_by_value(cls, value, default=None):
try:
return cls(value)
except ValueError:
return default
You can add also find_all_by_value(), get_aliases(), etc. It is
important that they are module-level function, so they do not spoil the
namespace of the Enum class.
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