Reading Coefs in Polynom (str to dict)

source.py

class Polynom:
    def __init__(self, s):
        self.coefs = self.reborn(s)

    def reborn(self, source):
        result = list()
        coefs = dict()

        source = source.split('+')

        for item in source:
            buffer = []
            for char in item:
                if char == '-':
                    if len(buffer):
                        result.append(buffer)
                    buffer = ['-']
                else:
                    buffer.append(char)
            if len(buffer):
                result.append(buffer)

        for item in result:
            wasX = False
            buffer = []
            isNowBase = True
            isNowPower = False

            base = 0
            power = 0

            for char in item:
                if char == 'x':
                    wasX = True
                elif char == '^':
                    isNowPower = True
                    isNowBase = False
                    if len(buffer):
                        base = int(''.join(buffer))
                    buffer = list()
                elif isNowBase:
                    if char.isdigit() or char == '-':
                        buffer.append(char)
                elif isNowPower:
                    if char.isdigit():
                        buffer.append(char)

            if len(buffer) and isNowPower:
                power += int(''.join(buffer))
            elif len(buffer) and isNowBase:
                base = int(''.join(buffer))

            if wasX:
                if power == 0:
                    power = 1
            else:
                power = 0

            coefs[power] = base

        return coefs

    def __str__(self):
        return str(self.coefs)


a = Polynom('123x^12+456x^13+789')
print(a)