Special Methods in Python
The built-in mathematical operators can be extended in much the same way as repr;
there are special method names corresponding to Python operators for arithmetic,
logical, and sequence operations.
To make our code more legible, we would perhaps like to use the + and * operators
directly when adding and multiplying complex numbers. Adding the following methods to
both of our complex number classes will enable these operators to be used, as well as
the add and mul functions in the operator module:
>>> ComplexRI.__add__ = lambda self, other:
add_complex(self, other)
>>> ComplexMA.__add__ = lambda self, other:
add_complex(self, other)
>>> ComplexRI.__mul__ = lambda self, other:
mul_complex(self, other)
>>> ComplexMA.__mul__ = lambda self, other:
mul_complex(self, other)
Now, we can use infix notation with our user-defined classes.
>>> ComplexRI(1, 2) + ComplexMA(2, 0)
ComplexRI(3.0, 2.0)
>>> ComplexRI(0, 1) * ComplexRI(0, 1)
ComplexMA(1.0, 3.141592653589793)
True and false values. We saw previously that numbers in Python have a truth value;
more specifically, 0 is a false value and all other numbers are true values. In fact, all
objects in Python have a truth value. By default, objects are considered to be true, but
the special __bool__ method can be used to override this behavior. If an object defines
the __bool__ method, then Python calls that method to determine its truth value.
As an example, suppose we want the complex number 0 + 0 * i to be false. We can
define the __bool__ method for both our complex number implementations.
