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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def credit_card_number(self, card_type: Optional[CardType] = None) -> str: """Generate a random credit card number. :param card_type: Issuing Network. Default is Visa. :return: Credit card number. :raises NotImplementedError: if cart_type is not supported. :Example: 4455 5299 1152 2450 """

        length = 16
        regex = re.compile(r'(\d{4})(\d{4})(\d{4})(\d{4})')

        if card_type is None:
            card_type = get_random_item(CardType, rnd=self.random)

        if card_type == CardType.VISA:
            number = self.random.randint(4000, 4999)
        elif card_type == CardType.MASTER_CARD:
            number = self.random.choice([
                self.random.randint(2221, 2720),
                self.random.randint(5100, 5599),
            ])
        elif card_type == CardType.AMERICAN_EXPRESS:
            number = self.random.choice([34, 37])
            length = 15
            regex = re.compile(r'(\d{4})(\d{6})(\d{5})')
        else:
            raise NonEnumerableError(CardType)

        str_num = str(number)
        while len(str_num) < length - 1:
            str_num += self.random.choice(string.digits)

        groups = regex.search(  # type: ignore
            str_num + luhn_checksum(str_num),
        ).groups()
        card = ' '.join(groups)
        return card