```
from enum import Enum

class T(Enum):
  TEST = 1

print(T["TEST"])

class S(Enum):
  TEST = lambda a: a

print(S["TEST"])
```
fails with `KeyError: 'TEST'` on the last line.

https://docs.python.org/3/library/enum.html#allowed-members-and-attributes-of-enumerations

> The rules for what is allowed are as follows: names that start and end with a single underscore are reserved by enum and cannot be used; all other attributes defined within an enumeration will become members of this enumeration, with the exception of special methods (__str__(), __add__(), etc.), descriptors (methods are also descriptors), and variable names listed in _ignore_.

Looking at the code _member_names has the list of member names internally that stores the members. I guess with a callable assigned to TEST it becomes a method and is not added as a member as per the above doc to skip descriptor as method.

Some relevant threads

* https://stackoverflow.com/questions/40338652/how-to-define-enum-values-that-are-functions
* https://mail.python.org/pipermail/python-ideas/2017-April/045428.html

This is the intended, and documented, behavior.

Where is this documented? Sorry, I couldn't find it.

In any case, I'd say this behaviour is quite unexpected, and unless technical reasons are overwhelming, would be nice to change it.