在加法运算中翻转参数的 Python 3 方法

Question

我有一个添加两个点的类（其中一个是 Point 类型，另一个是元组或列表——参见代码）。我的问题是我的 add 方法只有在我按特定顺序输入数字时才有效。我需要创建第二个方法（根据此作业中的规则），它只包含一行调用 add 方法并返回结果，并且可以在文档的数据模型中找到。 p>

class Point():
def __init__(self, x=0, y=0):
    self.x = x
    self.y = y

def __str__(self):
    return ("X = " + str(self.x) + "\nY = " + str(self.y))

def __add__(self, other):
    if isinstance(other,list) or isinstance(other,tuple):
        newX = other[0] + self.x
        newY = other[1] + self.y
        return(Point(newX,newY))
    else:
        newX = self.x + other
        newY = self.y + other
        return(Point(newX,newY))

p = Point(5,10)
print(p + [3.5,6])
print([3.5,6] + p)

我已经搜索了数据模型，我只能认为 reversed 或带有 getattr 的东西会起作用，但我不知道如何实现，或者如果我什至在正确的轨道上。请帮忙！

Answer 1

你应该在你的班级中添加__radd__()：

def __radd__(self, *args, **kwargs):
    return self.__add__(*args, **kwargs)

这实际上会执行__add__()，因为在这种情况下它确实是一样的。

但你可以考虑让这个类表现得像一个列表，像这样：

class Point():
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y
        self._list = [self.x, self.y]

    def __str__(self):
        return ("X = " + str(self.x) + "\nY = " + str(self.y))

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

    def __iter__(self):
        for elem in self._list:
            yield elem

    def __getitem__(self, i):
        return self._list(i)

    def __len__(self):
        return len(self._list)

    def __delitem__(self, i):
        #not sure if you really want this
        del self._list[i]

    def __setitem__(self, i, val):
        #not sure if you really want this
        self._list[i] = val    

    def __add__(self, other):
        #this code could be optimized
        #using your original code for this example
        if isinstance(other,list) or isinstance(other,tuple):
            newX = other[0] + self.x
            newY = other[1] + self.y
        else:
            newX = self.x + other
            newY = self.y + other
        #returning a list
        return [newX, newY]

    def __radd__(self, *args, **kwargs):
        return self.__add__(*args, **kwargs)


p = Point(5,10)
print(p)
print(p + [3.5,6])
print([3.5,6] + p)

输出：

[5, 10]
[8.5, 16]
[8.5, 16]

[编辑] 如果你决定让它表现得像 list，你也可以继承 list，例如：

class Point(list):

    def __init__(self, x=0, y=0):
        super(Point, self).__init__([x, y])

    def __add__(self, other):
        if isinstance(other, (list, tuple)):
            return [sum(i) for i in zip(self, other)]
        elif isinstance(other, (int, float)):
            return [i + other for i in self]
        else:
            return self

    def __radd__(self, *args, **kwargs):
        return self.__add__(*args, **kwargs)

    #you probably want a __sub__
    def __sub__(self, other):
        if isinstance(other, (list, tuple)):
            return [i - j for i, j in zip(self, other)]
        elif isinstance(other, (int, float)):
            return [i - other for i in self]
        else:
            return self

    #and an __rsub__
    def __rsub__(self, other):
        if isinstance(other, (list, tuple)):
            return [i - j for i, j in zip(other, self)]
        elif isinstance(other, (int, float)):
            return [other - i for i in self]
        else:
            return self   

    #take away functions you do not want
    def pop(*args, **kwargs): pass
    def sort(*args, **kwargs): pass
    def append(*args, **kwargs): pass
    def extend(*args, **kwargs): pass
    def insert(*args, **kwargs): pass
    def remove(*args, **kwargs): pass
    def reverse(*args, **kwargs): pass

p = Point(5,10)
tests = [[3.5, 6], (5,4), 1.1, 'wrong string', [1, 2, 3]]
for test in tests:
    print(p + test)
    print(test + p)
for test in tests:
    print(p - test)
    print(test - p)   
p.append(4)
print(p)

输出：

[8.5, 16]
[8.5, 16]
[10, 14]
[10, 14]
[6.1, 11.1]
[6.1, 11.1]
[5, 10]
[5, 10]
[6, 12]
[6, 12]
[1.5, 4]
[-1.5, -4]
[0, 6]
[0, -6]
[3.9, 8.9]
[-3.9, -8.9]
[5, 10]
[5, 10]
[4, 8]
[-4, -8]
[5, 10]