'Handle object conversion if input is an instance of lti.'

def __new__(cls, *system, **kwargs):

    if ((len(system) == 1) and isinstance(system[0], LinearTimeInvariant)):
        return system[0].to_tf()
    if (cls is TransferFunction):
        if (kwargs.get('dt') is None):
            return TransferFunctionContinuous.__new__(TransferFunctionContinuous, *system, **kwargs)
        else:
            return TransferFunctionDiscrete.__new__(TransferFunctionDiscrete, *system, **kwargs)
    return super(TransferFunction, cls).__new__(cls)
