The __add__ method
__add__(self, other)
These methods are called to implement the binary arithmetic operations
(+, -, \*, //, %, divmod(), pow(), \*\*, <``<, `
>`>, &, ^, |). For instance, to evaluate the
expression x+y, where x is an instance of a class that has an
__add__ method, x.\_\_add\_\_(y) is called. The
__divmod__ method should be the equivalent to using
__floordiv__ and __mod__; it should not be related to
__truediv__ (described below). Note that __pow__ should be
defined to accept an optional third argument if the ternary version of
the built-in pow function is to be supported.