code: def execute_before(self, sensor_graph, scope_stack):
          
  
          sensor_graph.add_constant(self.stream, 0)
  
          new_scope = GatedClockScope(sensor_graph, scope_stack, (self.stream, self.trigger))
          scope_stack.append(new_scope)
docs: Execute statement before children are executed.
  
          Args:
              sensor_graph (SensorGraph): The sensor graph that we are building or
                  modifying
              scope_stack (list(Scope)): A stack of nested scopes that may influence
                  how this statement allocates clocks or other stream resources.