<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def full_number(self):
 """ Returns the full number including the verification digit. :return: str """

        return '{}{}'.format(
            ''.join(str(n) for n in self.numbers),
            ReceiptBarcodeGenerator.verification_digit(self.numbers),
        )