enum.Enum
https://docs.python.org/ja/3/library/enum.html#enum.Enum
#Python_enum
メンバーのnameやvalueはここで実装されている
__repr__
By default, returns the Enum name, member name, and value, but can be overridden:
__str__
By default, returns the Enum name and member name, but can be overridden: