import re

class Result:
    def __init__(self, value=[], start=0, end=0):
        print('INIT:', value)
        if value == ['a', 'b']:
            raise
        self.value = value
        self.start = start
        self.end = end

class Expression:
    def __init__(self, regex):
        self.regex = regex
        self.pattern = re.compile(self.regex)
        
    def match(self, s, offset=0):
        match = self.pattern.match(s, offset)
        if match:
            return Result([match.group(0)], match.start, match.end())
        
        
class Group:
    def __init__(self):
        self.__children = []
    
    def register(self, el):
        self.__children.append(el)
        
    def match(self, s, offset=0):
        match = None
        result = Result()
        print('!!!',Result().value)
        result.start = offset
        result.end = offset
        for child in self.__children:
            match = child.match(s, result.end)
            if not match:
                return None
            result.value += match.value
            result.end = match.end
        return result
    
class Range:
    def __init__(self, child, count=1):
        self.__count = count
        self.__child = child
        
    def match(self, s, offset=0):
        child = self.__child
        result = Result([],offset,offset)
        for i in range(self.__count):
            print('>>',i)
            match = child.match(s, result.end)
            if not match:
                return None
            result.end = match.end
            result.value += match.value
        return result
    
a = Expression('a')
b = Expression('b')
g=Group()
g.register(a)
g.register(b)
r = Range(g,2)
x = r.match('abab') 
print(x)