code: def find_sink_variables(self):
          '''
          Find sink variables in this scope
          '''
          # First we assume all variables are sinks
          is_sink = {name: True for name in self.variables.keys()}
          # Then, we remove those variables which are inputs of some operators
          for operator in self.operators.values():
              for variable in operator.inputs:
                  is_sink[variable.onnx_name] = False
          return [variable for name, variable in self.variables.items() if is_sink[name]f find_sink_variables(self):
          '''
          Find sink variables in this scope
          '''
          # First we assume all variables are sinks
          is_sink = {name: True for name in self.variables.keys()}
          # Then, we remove those variables which are inputs of some operators
          for operator in self.operators.values():
              for variable in operator.inputs:
                  is_sink[variable.onnx_name] = False
          return [variable for name, variable in self.variables.items() if is_sink[name]]
docs: Find sink variables in this scope