Question

HI

Trying to understand how __radd__ works. I have the code

>>> class X(object):
    def __init__(self, x):
        self.x = x
    def __radd__(self, other):
        return X(self.x + other.x)


>>> a = X(5)
>>> b = X(10)
>>> a + b

Traceback (most recent call last):
  File "<pyshell#8>", line 1, in <module>
    a + b
TypeError: unsupported operand type(s) for +: 'X' and 'X'
>>> b + a

Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    b + a
TypeError: unsupported operand type(s) for +: 'X' and 'X'

Why is this not working? What am I doing wrong here?

Answer 1

Python docs for operators

“These functions are only called if the left operand does not support the corresponding operation and the operands are of different types.”

See also Footnote 2

Since the operands are of the same type, you need to define __add__.