[Python] Python: How to check what types are in defined types.UnionType?

I am using Python 3.11 and I would need to detect if an optional class attribute is type of Enum (i.e. type of a subclass of Enum).

With typing.get_type_hints() I can get the type hints as a dict, but how to check if a field's type is optional Enum (subclass)? Even better if I could get the type of any optional field regardless is it Optional[str], Optional[int], Optional[Class_X], etc.

Example code


from typing import Optional, get_type_hints
from enum import IntEnum, Enum

class TestEnum(IntEnum):
foo = 1
bar = 2


class Foo():
opt_enum : TestEnum | None = None

types = get_type_hints(Foo)['opt_enum']

This works


(ipython)

In [4]: Optional[TestEnum] == types
Out[4]: True

These ones fail


(yes, these are desperate attempts)

In [6]: Optional[IntEnum] == types
Out[6]: False


and

In [11]: issubclass(Enum, types)
Out[11]: False


and

In [12]: issubclass(types, Enum)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In [12], line 1
----> 1 issubclass(types, Enum)

TypeError: issubclass() arg 1 must be a class


and

In [13]: issubclass(types, Optional[Enum])
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In [13], line 1
----> 1 issubclass(types, Optional[Enum])

File /usr/lib/python3.10/typing.py:1264, in _UnionGenericAlias.__subclasscheck__(self, cls)
1262 def __subclasscheck__(self, cls):
1263 for arg in self.__args__:
-> 1264 if issubclass(cls, arg):
1265 return True

TypeError: issubclass() arg 1 must be a class


and

In [7]: IntEnum in types
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
Cell In [7], line 1
----> 1 IntEnum in types

TypeError: argument of type 'types.UnionType' is not iterable

Why I needed this


I have several cases where I am importing data from csv files and creating objects of a class from each row. csv.DictReader() returns a dict[str, str] and I need to fix the types for the fields before attempting to create the object. However, some of the object fields are Optional[int], Optional[bool], Optional[EnumX] or Optional[ClassX]. I have several of those classes multi-inheriting my CSVImportable() class/interface. I want to implement the logic once into CSVImportable() class instead of writing roughly same code in field-aware way in every subclass. This CSVImportable._field_type_updater() should:

1. correctly change the types at least for basic types and enums
2. Gracefully skip Optional[ClassX] fields

Naturally I am thankful for better designs too

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