encode and decode from decimal system to alphabet numeric system and reverse

numCode.py

class numCode:
    characters = list('abcdefghijklmnopqrstuvwxyz')
        
    def __init__(self,**kwargs):
        self.characters = list('abcdefghijklmnopqrstuvwxyz')
        
        if 'characters' in kwargs.keys():
            self.characters = kwargs['characters']
            
    @classmethod
    def encode(cls,i):
        calosc = int(i / len(cls.characters))
        reszta = i % len(cls.characters)
        if calosc > 0:
            return cls.encode(calosc) + cls.characters[reszta]
        else:
            return cls.characters[reszta]
            
    @classmethod
    def decode(cls,i):
        number = 0
        array = list(i)
        array.reverse()
        for index,char in enumerate(array):
            number += len(cls.characters)**index *(cls.characters.index(char))
        return number