polynominal.py

import re

POSITIVE = True
NEGATIVE = False


class Term():
    def __init__(self, coefficient, power):
        self.coefficient = coefficient
        self.power = power

    def evaluate(self, value):
        return value**self.power * self.coefficient

    def __str__(self):
        return '{}x{}'.format(self.coefficient, self.power)

    def __repr__(self):
        return 'Term({})'.format(self.__str__())


class Polynominal():
    def __init__(self, *terms):
        self.terms = terms

    def evaluate(self, value):
        result = 0
        for term in self.terms:
            result += term.evaluate(value)
        return result

    def __str__(self):
        return ' '.join(str(i) for i in self.terms)

    def __repr__(self):
        return 'Polynominal({})'.format(self.__str__())


def parse_term(term, sign):
    if 'x' in term:
        term = term.split('x')
    else:
        term = [term]

    coefficient = 1
    if term[0] != '':
        coefficient = float(term[0])

    power = 1
    if len(term) == 2 and term[1] != '':
        power = int(term[1])
    elif len(term) == 1:
        power = 0

    if sign == NEGATIVE:
        coefficient *= -1
    return Term(coefficient, power)


def parse_poly(poly):
    poly = re.split(r'([-\+])', poly)
    poly = [i.strip() for i in poly]
    processed = []

    # process first term by itself
    first_term = poly[0]
    if first_term[0] == '-':
        first_term = parse_term(first_term[:1], NEGATIVE)
    else:
        first_term = parse_term(first_term, POSITIVE)
    processed.append(first_term)

    # process the remainder
    for i in range(1, len(poly), 2):
        sign = POSITIVE if poly[i] == '+' else NEGATIVE
        term = poly[i + 1]
        processed.append(parse_term(term, sign))
    return Polynominal(*processed)