Explicitly disable pickling CachedSession objects

Fixes #707 (for 0.9)

HISTORY.md

@@ -1,20 +1,26 @@
 # History
 
 ## 0.9.7 (Unreleased)
+Backport fixes from 1.0:
 * Fix potential `AttributeError` due to undetected imports when requests-cache is bundled in a PyInstaller package
+* Fix `AttributeError` when attempting to unpickle a `CachedSession` object, and instead disable
+  pickling by raising a `NotImplementedError`
 * Update to cattrs 22.2
 
 ## 0.9.6 (2022-08-24)
+Backport fixes from 1.0:
 * Remove potentially problematic row count from `BaseCache.__str__()`
 * Remove upper version constraints for all non-dev dependencies
 * Make dependency specification consistent between PyPI and Conda-Forge packages
 
 ## 0.9.5 (2022-06-29)
+Backport fixes from 1.0:
 * Fix usage of memory backend with `install_cache()`
 * Add `CachedRequest.path_url` property
 * Add compatibility with cattrs 22.1
 
 ## 0.9.4 (2022-04-22)
+Backport fixes from 1.0:
 * Fix forwarding connection parameters passed to `RedisCache` for redis-py 4.2 and python <=3.8
 * Fix forwarding connection parameters passed to `MongoCache` for pymongo 4.1 and python <=3.8
 

requests_cache/session.py

@@ -280,6 +280,12 @@ def remove_expired_responses(self, expire_after: ExpirationTime = None):
         """
         self.cache.remove_expired_responses(expire_after)
 
+    def __getstate__(self):
+        # Unlike requests.Session, CachedSession may contain backend connection objects that can't
+        # be pickled. Support for this could be added if necessary, but for now it's explicitly
+        # disabled to avoid confusing errors upon unpickling.
+        raise NotImplementedError('CachedSession cannot be pickled')
+
     def __repr__(self):
         repr_attrs = [
             'cache',

tests/unit/test_session.py

@@ -1,6 +1,7 @@
 """CachedSession + BaseCache tests that use mocked responses only"""
 # TODO: This could be split up into some smaller test modules
 import json
+import pickle
 import time
 from collections import UserDict, defaultdict
 from datetime import datetime, timedelta
@@ -78,6 +79,11 @@ def test_init_backend_class():
     assert session.cache.cache_name == 'test_cache'
 
 
+def test_pickle__disabled():
+    with pytest.raises(NotImplementedError):
+        pickle.dumps(CachedSession(backend='memory'))
+
+
 @pytest.mark.parametrize('method', ALL_METHODS)
 @pytest.mark.parametrize('field', ['params', 'data', 'json'])
 def test_all_methods(field, method, mock_session):