def collect self parts sizes items_sizes self calculate_ratio sizes su

    def collect(self, parts, sizes):
        items_sizes = self.calculate_ratio(sizes, sum(map(len, parts)))
        result = []
        atoms = map(list, parts)
        for index, size in enumerate(items_sizes):
            result.append(''.join(atoms[index][:size]))
            del atoms[index][:size]
        result = ''.join(result) 
        while any(atoms):
            for x in filter(bool, atoms):
                result += x[0]
                del x[0]
        return result