7.4 Magic methods

You do not call the three methods __init__, __repr__, and __str__ directly; Python “magically” calls them for you when it needs to initialize an instance, get an input representation, or convert to a string. You can define several dozen such “magic methods” with predefined uses. The algebraic and comparison methods are important to us for polynomials, so let’s look at some examples.

7.4.1 Negation

I now define negation via __neg__, where I create a new polynomial by applying “-” to each coefficient. In this third version of UniPoly, I extend __init__ to accept a coefficient and exponent.

class UniPoly:
    # UniPoly creates univariate polynomials with integer coefficients
    # Version 3

    def __init__(self,
                 coefficient=1,
                 indeterminate='x',
                 exponent=0):

        # Create a UniPoly object from...