Using __add__ operator with multiple arguments in Python

问题

I am trying to add a class object with a number, but I'm confused on how to go about adding a class object with two numbers. For example, this is my hypothetical add class method:

class A:
    def __add__(self, b):
        return something

I know how to add this so far:

object = A()
print(object + 1)

But, what if I want to add it like this?

object = A()
print(object + 1 + 2)

Should I use *args for the add class method?

回答1:

No, you can't use multiple arguments. Python executes each + operator separately, the two + operators are distinct expressions.

For your example, object + 1 + 2 really is (object + 1) + 2. If (object + 1) produces an object that has an __add__ method, then Python will call that method for the second operator.

You could, for example, return another instance of A here:

>>> class A:
...     def __init__(self, val):
...         self.val = val
...     def __repr__(self):
...         return f'<A({self.val})>'
...     def __add__(self, other):
...         print(f'Summing {self} + {other}')
...         return A(self.val + other)
...
>>> A(42) + 10
Summing A(42) + 10
<A(52)>
>>> A(42) + 10 + 100
Summing A(42) + 10
Summing A(52) + 100
<A(152)>

回答2:

You would want your return value to be an object itself, that also supports the add operation, e.g.:

class A:
    def __init__(self, value=0):
        self.value = value

    def __add__(self, b):
        return A(self.value + b)

    def __str__(self):
        return str(self.value)

a = A()
print(a + 1 + 2)

Output:

3

回答3:

It perfectly works even with multiple values since each add only adds two values (see the multiple + signs when you ad multiple values):

class A:
    def __init__(self, value):
        self.a = value
    def __add__(self, another_value):
        return self.a + another_value


a = A(1)
print(a+1+1)

来源：https://stackoverflow.com/questions/46885618/using-add-operator-with-multiple-arguments-in-python

标签

python

class

overloading

add

operator-keyword