TypeError: Invalid first argument to register(). ForwardRef('CachedResponse') is not a class.

[glensc]

The problem

Such error has emerged: Taxel/PlexTraktSync#740

$ python -c "from requests_cache import CachedSession"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/python-3.9.10/lib/python3.9/site-packages/requests_cache/__init__.py", line 43, in <module>
    from .backends import *
  File "/python-3.9.10/lib/python3.9/site-packages/requests_cache/backends/__init__.py", line 8, in <module>
    from .base import BaseCache, BaseStorage
  File "/python-3.9.10/lib/python3.9/site-packages/requests_cache/backends/base.py", line 18, in <module>
    from ..serializers import init_serializer
  File "/python-3.9.10/lib/python3.9/site-packages/requests_cache/serializers/__init__.py", line 6, in <module>
    from .preconf import (
  File "/python-3.9.10/lib/python3.9/site-packages/requests_cache/serializers/preconf.py", line 26, in <module>
    base_stage = CattrStage()  #: Base stage for all serializer pipelines
  File "/python-3.9.10/lib/python3.9/site-packages/requests_cache/serializers/cattrs.py", line 32, in __init__
    self.converter = init_converter(factory)
  File "/python-3.9.10/lib/python3.9/site-packages/requests_cache/serializers/cattrs.py", line 68, in init_converter
    converter.register_structure_hook(
  File "/python-3.9.10/lib/python3.9/site-packages/cattr/converters.py", line 269, in register_structure_hook
    self._structure_func.register_cls_list([(cl, func)])
  File "/python-3.9.10/lib/python3.9/site-packages/cattr/dispatch.py", line 57, in register_cls_list
    self._single_dispatch.register(cls, handler)
  File "/usr/local/Cellar/python@3.9/3.9.10/Frameworks/Python.framework/Versions/3.9/lib/python3.9/functools.py", line 855, in register
    raise TypeError(
TypeError: Invalid first argument to `register()`. ForwardRef('CachedResponse') is not a class.

Environment

• requests 2.27.1
• requests-cache 0.8.1
• cattrs 1.10.0
• Python version: 3.9.9, 3.9.10, 3.10.0
• Platform: macOS, Windows

[glensc]

Something odd is happening, started to work with 3.9.9, 3.10.1. I was just switching versions of python trying to figure out what version has the breakage. now upgraded to Python 3.9.10 and it's broken again. I compared site-packagers of two versions, did not see any obvious differences...

[JWCook]

See #501; there was an unexpected breaking change in functools in python 3.10.2 and 3.9.10. A fix has been released in requests-cache 0.9.1.