import random


def generate_credit_card(card_type=None):
	"""
	Function to generate the credit card number of the profile.

	Args:
		card_type: String value, either "Visa" or "Mastercard". (optional)

	Returns:
		The return value. String value containing credit card number.

	"""
	if not card_type:
		card_type = random.choice(['VISA', 'Mastercard'])
	if card_type.lower() == "visa":
		return '4'+str(random.randint(123242323223432,986879876876876))
	elif card_type.lower() == "mastercard":
		return '5'+str(random.randint(123242323223432,986879876876876))