import mathclass Measurement(object):    def __init__(self, val, perc):        self.val = val        self.perc = perc        self.abs  = self.val * self.perc / 100.0    def __repr__(self):        return "Measurement (%r, %r)" % (self.val, self.perc)    def __str__(self):        return "%g+-%g%%" % (self.val, self.perc)    def _addition_result(self, result, other_abs):        new_perc = 100.0 *(math.hypot(self.abs, other_abs) / result)        return Measurement(result, new_perc)    def __add__(self, other):        result = self.val + other.val        return self._addition_result(result, other.abs)    def __sub__(self, other):        result = self.val - other.val        return self._addition_result( result, other.abs)    def _multiplication_result(self, result, other_perc):        new_perc = math.hypot(self.perc, other_perc)        return Measurement(result, new_perc)    def __mul__(self, other):        result = self.val * other.val        return self._multiplication_result(result, other.perc)    def __div__(self, other):        result = self.val / other.val        return self._multiplication_result(result, other.perc)m1 = Measurement(100.0, 5.5)m2 = Measurement(50, 2)print "m1 = " , m1print "m2 = ",  m2print "m1 + m2 = ", m1 + m2print "m1 - m2 = ", m1 - m2print "m1 * m2 = ", m1 * m2print "m1 / m2 = ", m1 / m2print "(m1+m2) *(m1-m2) = " ,(m1+m2) * (m1-m2)print "(m1+m2) / (m1+m2) = ", (m1-m2) / (m1+m2)