allow for roundtrip of cloudpaths through pickle serialization

This avoids an exception thrown because the client is not serialized
into the pickeld object, and thus when __getstate__ is called the second
time, there is no _client field to delete.

Closes #450

cloudpathlib/cloudpath.py

@@ -263,7 +263,8 @@ def __getstate__(self) -> Dict[str, Any]:
         state = self.__dict__.copy()
 
         # don't pickle client
-        del state["_client"]
+        if "_client" in state:
+            del state["_client"]
 
         return state
 

tests/test_cloudpath_serialize.py

@@ -0,0 +1,14 @@
+import pickle
+
+from cloudpathlib import CloudPath
+
+
+def test_pickle_roundtrip():
+    path1 = CloudPath("s3://bucket/key")
+    pkl1 = pickle.dumps(path1)
+
+    path2 = pickle.loads(pkl1)
+    pkl2 = pickle.dumps(path2)
+
+    assert path1 == path2
+    assert pkl1 == pkl2