[pymongo] Fix multiple host kwarg (#535)

* [pymongo] replicate multiple kwarg from #369
* [pymongo] fix for multiple kwarg host bug

Author: Kyle-Verhoog

ddtrace/contrib/pymongo/client.py

@@ -40,9 +40,22 @@ def __init__(self, client=None, *args, **kwargs):
         # To support the former trace_mongo_client interface, we have to keep this old interface
         # TODO(Benjamin): drop it in a later version
         if not isinstance(client, _MongoClient):
-            # Patched interface, instanciate the client
-            # Note that, in that case, the client argument isn't a client, it's just the first arg
-            client = _MongoClient(client, *args, **kwargs)
+            # Patched interface, instantiate the client
+
+            # client is just the first arg which could be the host if it is
+            # None, then it could be that the caller:
+
+            # if client is None then __init__ was:
+            #   1) invoked with host=None
+            #   2) not given a first argument (client defaults to None)
+            # we cannot tell which case it is, but it should not matter since
+            # the default value for host is None, in either case we can simply
+            # not provide it as an argument
+            if client is None:
+                client = _MongoClient(*args, **kwargs)
+            # else client is a value for host so just pass it along
+            else:
+                client = _MongoClient(client, *args, **kwargs)
 
         super(TracedMongoClient, self).__init__(client)
         # NOTE[matt] the TracedMongoClient attempts to trace all of the network

tests/contrib/pymongo/test.py

@@ -280,6 +280,20 @@ def test_service(self):
         assert s['app_type'] == 'db'
         assert s['app'] == 'mongodb'
 
+    def test_host_kwarg(self):
+        # simulate what celery and django do when instantiating a new client
+        conf = {
+            'host': 'localhost'
+        }
+        client = pymongo.MongoClient(**conf)
+
+        conf = {
+            'host': None
+        }
+        client = pymongo.MongoClient(**conf)
+
+        assert client
+
 
 class TestPymongoPatchConfigured(PymongoCore):
     """Test suite for pymongo with a configured patched library"""