DOC add note to warn about running basic example with an asyncio event loop running (#116)

Small fixes for the assertion messages

Author: leszekhanusz

README.md

@@ -63,6 +63,10 @@ result = client.execute(query)
 print(result)
 ```
 
+> **WARNING**: Please note that this basic example won't work if you have an asyncio event loop running. In some
+> python environments (as with Jupyter which uses IPython) an asyncio event loop is created for you. In that case you
+> should use instead the example in the [AIOHTTPTransport](#HTTP-async-transport) section.
+
 ### Local schema validation
 
 It is possible to validate a query locally either using a provided schema or by using

gql/client.py

@@ -113,8 +113,8 @@ def execute(self, document: DocumentNode, *args, **kwargs) -> Dict:
             loop = asyncio.get_event_loop()
 
             assert not loop.is_running(), (
-                "Cannot run client.execute if an asyncio loop is running."
-                " Use execute_async instead."
+                "Cannot run client.execute(query) if an asyncio loop is running."
+                " Use 'await client.execute_async(query)' instead."
             )
 
             data: Dict[Any, Any] = loop.run_until_complete(
@@ -151,8 +151,8 @@ def subscribe(
         loop = asyncio.get_event_loop()
 
         assert not loop.is_running(), (
-            "Cannot run client.subscribe if an asyncio loop is running."
-            " Use subscribe_async instead."
+            "Cannot run client.subscribe(query) if an asyncio loop is running."
+            " Use 'await client.subscribe_async(query)' instead."
         )
 
         try:
@@ -199,9 +199,10 @@ async def __aexit__(self, exc_type, exc, tb):
 
     def __enter__(self):
 
-        assert not isinstance(
-            self.transport, AsyncTransport
-        ), "Only a sync transport can be use. Use 'async with Client(...)' instead"
+        assert not isinstance(self.transport, AsyncTransport), (
+            "Only a sync transport can be used."
+            " Use 'async with Client(...) as session:' instead"
+        )
 
         self.transport.connect()