Polynomial Class in Python

Thinking about orthogonal polynomials over the past couple days made me curious about creating a class definition in Python that would allow one to do simple polynomial calculations (e.g. addition, multiplication, evaluation). I struggled a little bit with creating an elegant solution for polynomial multiplication. I settled on a double loop, but I am wondering if anyone has a nicer solution, please share!

from operator import add 

class Polynomial(object):
    def __init__(self, coeffs):
        self.degree = len(coeffs) - 1
        self.rep = self.__str(coeffs)
        self.coefficients = coeffs
    def __repr__(self):
        return self.rep
    def __str(self, coeffs):
        #Create list of nonzero terms
        terms = [' + ' + str(coeffs[k]) + 'x**' \
                + str(k) \
                for k in range(0, self.degree + 1) \
                if coeffs[k] <> 0]
        #If zero polynomial, return 0
        if len(terms) == 0:
            return str(0)
        #Otherwise concatenate terms 
        p = reduce(add, terms)
        #Strip out leading +
        return p.lstrip(' + ')
    def __add(self, other):
        """Adds two polynomials."""
        #Max length of polynomials' coeff lists
        d = max(self.degree, other.degree) + 1
        #Pad coeffs lists with 0s until equal length
        self_temp = self.coefficients + [0]*(d-self.degree-1)
        other_temp = other.coefficients + [0]*(d-other.degree-1)
        #Sum coeffs lists elementwise
        return Polynomial(map(add, self_temp, other_temp))
    def __mul(self, other):
        """Multiplies two polynomials."""
        n = self.degree + other.degree     #Degree of product
        prod_coeffs = [0]*(n+1) #Initalize coefficient list of product
        #Compute Cauchy product
        for i in range(0, self.degree + 1):
            for j in range(0, other.degree + 1):
                prod_coeffs[i+j] += self.coefficients[i] * other.coefficients[j]
        return Polynomial(prod_coeffs)
    def __add__(self, other):
        """Overloads the + operator."""
        return self.__add(other)
    def __mul__(self, other):
        """Overloads the * operator."""
        return self.__mul(other)
    def __call__(self, val):
        """Evaluates the polynomial at x = val."""
        sum = 0
        return reduce(add, [self.coefficients[i]*(val**i) \
                            for i in range(self.degree +  1)])
This entry was posted in math.AC, Progamming, Python and tagged , , , , . Bookmark the permalink.

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