def _dpow(x, y, n):
 if (n < 0):
  raise ValueError('invalid derivative order')
 elif (n > y):
  return 0
 else:
  return (poch(((y - n) + 1), n) * (x ** (y - n)))

def _dpow ( x , y , n ) : if ( n < 0 ) : raise ValueError ( 'invalid derivative order' ) elif ( n > y ) : return 0 else : return ( poch ( ( ( y - n ) + 1 ) , n ) * ( x ** ( y - n ) ) )
d^n / dx^n .