Clean & Pythonic Code

[suffixing]

if isinstance(value, list):
    return cls(*[getattr(cls, val.upper()) for val in value])

return getattr(cls, value.upper(), super()._missing_(value))

replaced if statements with a getattr() call, converts the input to uppercase, and used a list comprehension

return getattr(cls, value.upper(), super()._missing_(value))

return the attribute with given value using getattr(). If the attribute is not found, it falls back to the default _missing_ implementation.