PYTHON-1915 Prohibit copying ClientSession objects (#726)

doc/contributors.rst

@@ -89,4 +89,5 @@ The following is a list of people who have contributed to
 - Paul Fisher (thetorpedodog)
 - Julius Park (juliusgeo)
 - Khanh Nguyen (KN99HN)
-- Henri Froese (henrifroese)
+- Henri Froese (henrifroese)
+- Ishmum Jawad Khan (ishmum123)

pymongo/client_session.py

@@ -953,6 +953,9 @@ class ClientSession(object):
             if self._snapshot_time is not None:
                 rc['atClusterTime'] = self._snapshot_time
 
+    def __copy__(self):
+        raise TypeError('A ClientSession cannot be copied, create a new session instead')
+
 
 class _ServerSession(object):
     def __init__(self, generation):

test/test_session.py

@@ -716,6 +716,10 @@ class TestSession(IntegrationTest):
                                            snapshot=True):
                 pass
 
+    def test_session_not_copyable(self):
+        client = self.client
+        with client.start_session() as s:
+            self.assertRaises(TypeError, lambda: copy.copy(s))
 
 class TestCausalConsistency(unittest.TestCase):