Use a tuple for history

Author: Golf Player

nbclient/client.py

@@ -309,7 +309,7 @@ def __init__(self, nb, km=None, **kw):
         }
 
     def _update_state(self, new_state):
-        self.state_history.append([new_state, timestamp()])
+        self.state_history.append((new_state, timestamp()))
 
     def reset_execution_trackers(self):
         """Resets any per-execution trackers.
@@ -323,7 +323,8 @@ def reset_execution_trackers(self):
         self.output_hook_stack = collections.defaultdict(list)
         # our front-end mimicing Output widgets
         self.comm_objects = {}
-        self.state_history = [ExecutionState.IDLE, timestamp()]
+        self.state_history = []
+        self._update_state(ExecutionState.IDLE)
         self.current_cell = None
         self.current_cell_index = -1