如何在python中使用该方法[关闭]

Question

# Rational numbers

def gcd(bigger, smaller):
    '''compute the greatest common divisor of two positive integers'''
    #print(' in gcd ')
    if not bigger > smaller :
        bigger, smaller = smaller, bigger
    while smaller != 0:
        remainder = bigger % smaller
        #print('gcd calc, big:{}, small:{}, rem:{}'.format(bigger, smaller, remainder))
        bigger, smaller = smaller, remainder
    return bigger

def lcm(a, b):
    '''calculate the least common multiple of two positive integers'''
    #print(' in lcm ')
    return (a*b)//gcd(a,b)


class Rational(object):
    '''Rational with numerator and denominator. Denominator defaults to 1'''

    def __init__(self, numer, denom = 1):
        #print('in constructor')
        self.numer = numer
        self.denom = denom

    def __str__(self):
        '''String representation for printing'''
        #print(' in str ')
        return str(self.numer)  + '/'  +  str(self.denom)

    def __repr__(self):
        ''' Used in the interpreter. Call __str__ for now'''
        print(' in repr ')
        return self.__str__()

    def __add__(self, param_Rational):
        '''Add two Rationals'''
        if type(param_Rational) == int:
            param_Rational = Rational(param_Rational)
        if type(param_Rational) == Rational:
            # find the lcm
            the_lcm = lcm(self.denom, param_Rational.denom)
            # multiply each numerator by the lcm, then add
            numerator_sum = the_lcm*self.numer/self.denom + \
                        the_lcm*param_Rational.numer/param_Rational.denom
            return Rational( int(numerator_sum), the_lcm )
        else:
            print("Wrong type in addition method.")
            raise(TypeError)

    def __sub__(self, param_Rational):
        '''Subtract two Rationals'''
        #print(' in add ')
        # find the lcm
        the_lcm = lcm(self.denom, param_Rational.denom)
        # multiply each numerator by the lcm, then add
        numerator_sum = the_lcm*self.numer/self.denom - \
                    the_lcm*param_Rational.numer/param_Rational.denom
        return Rational( int(numerator_sum), the_lcm )

    def reduce_rational(self):
        '''Return the reduced fraction value as a Rational'''
        # find the gcd and divide numerator and denominator by it
        the_gcd = gcd(self.numer, self.denom)
        return Rational( self.numer//the_gcd, self.denom//the_gcd)

    def __eq__(self, param_Rational):
        '''Compare two Rationals for equalit and return a Boolean'''
        reduced_self  = self.reduce_rational()
        reduced_param = param_Rational.reduce_rational()
        return reduced_self.numer == reduced_param.numer and\
               reduced_self.denom == reduced_param.denom

如何调用 sub 和 add 方法来加/减任意两个有理数？

Answer 1

你不打电话给他们。当您用- 减去Rationals 或用+ 添加它们时，Python 会为您调用它们。 IE。在@Selcuk 的例子中：

print Rational(5,2) - Rational(1,3)

这将调用__sub__()