def butter(N, Wn, btype='low', analog=False, output='ba'):
 return iirfilter(N, Wn, btype=btype, analog=analog, output=output, ftype='butter')

def butter ( N , Wn , btype = 'low' , analog = False , output = 'ba' ) : return iirfilter ( N , Wn , btype = btype , analog = analog , output = output , ftype = 'butter' )
butterworth digital and analog filter design .