parameters: (self)
docstring: Convert to `TransferFunction` system, without copying.
  
          Returns
          -------
          sys: ZerosPolesGain
              The `TransferFunction` system. If the class is already an instance of
              `TransferFunction` then this instance is returned.
docstring_summary: Convert to `TransferFunction` system, without copying.
docstring_tokens: Convert to TransferFunction system without copying .
function: def _as_tf(self):
          """Convert to `TransferFunction` system, without copying.
  
          Returns
          -------
          sys: ZerosPolesGain
              The `TransferFunction` system. If the class is already an instance of
              `TransferFunction` then this instance is returned.
          """
          if isinstance(self, TransferFunction):
              return self
          else:
              return self.to_tf()
function_tokens: def _as_tf ( self ) : if isinstance ( self , TransferFunction ) : return self else : return self . to_tf ( )