code: def execute_before(self, sensor_graph, scope_stack):
          
  
          parent = scope_stack[-1]
          new_scope = TriggerScope(sensor_graph, scope_stack, parent.clock(self.interval, basis=self.basis))
          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.