字符串插值期间自定义添加方法失败

Question

#it's python 3.2.3
class point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __add__(self, point):
        self.x += point.x
        self.y += point.y
        return self

    def __repr__(self):
        return 'point(%s, %s)' % (self.x, self.y)

class Test:
    def __init__(self):
        self.test1 = [point(0, i) for i in range(-1, -5, -1)]
        self.test2 = [point(i, 0) for i in range(-1, -5, -1)]

        print('%s\n+\n%s\n=\n%s' % (self.test1[0], self.test2[0], self.test1[0] + self.test2[0]))

test = Test()
input()

这个程序的输出是

point(-1, -1)
+
point(-1, 0)
=
point(-1, -1)

但它应该是

point(-1, -1)
+
point(-1, 0)
=
point(-2, -1)

但如果我这样做

print(point(-1, -1) + point(-1, 0))

它完美地运作

我想知道为什么,以及如何解决这个问题

抱歉,如果我的英语不好:)

Answer 1

您的__add__函数将左侧参数修改为+.例如:

>>> x = point(0, 0)

>>> x + point(1, 1)
point(1, 1)

>>> x
point(1, 1)

你应该改变__add__要像

def __add__(self, oth):
    return point(self.x + oth.x, self.y + oth.y)