python - 当类实例位于右侧时，如何让我的类控制加法操作？

Question

这个问题已经有答案了:

TypeError after overriding the __add__ method (5 个回答)

已关闭 6 年前。

考虑我的类(class)mint

class mint(object):
    def __init__(self, i):
        self.i = i

    def __add__(self, other):
        o = other.i if isinstance(other, mint) else other
        return mint(1 + self.i + o)

    def __repr__(self):
        return str(self.i)

它的设计目的是进行另一种加法。

a = mint(1)

a + 1 + 2

6

但是，当我的对象位于右侧时添加不起作用。

1 + a

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-519-8da568c0620a> in <module>()
----> 1 1 + a

TypeError: unsupported operand type(s) for +: 'int' and 'mint'

<小时/>

问题:如何修改我的类，以便 1 + a会起作用吗？

Answer 1

您可以使用__radd__ :

class mint(object):
    def __init__(self, i):
        self.i = i

    def __add__(self, other):
        o = other.i if isinstance(other, mint) else other
        return mint(1 + self.i + o)

    def __repr__(self):
        return str(self.i)

    def __radd__(self, other):
        return self + other

a = mint(1)
print(1 + a)

输出:

3

以下是 Python 文档的解释:

These methods are called to implement the binary arithmetic operations (+, -, *, @, /, //, %, divmod(), pow(), **, <<, >>, &, ^, |) with reflected (swapped) operands. These functions are only called if the left operand does not support the corresponding operation and the operands are of different types. [2] For instance, to evaluate the expression x - y, where y is an instance of a class that has an rsub() method, y.rsub(x) is called if x.sub(y) returns NotImplemented.