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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 subscription(self):
 		""" 		Shortcut to get this customer's subscription. 		:returns: None if the customer has no subscriptions, the subscription if 			the customer has a subscription. 		:raises MultipleSubscriptionException: Raised if the customer has multiple subscriptions. 			In this case, use ``Customer.subscriptions`` instead. 		"""


		subscriptions = self.valid_subscriptions

		if subscriptions.count() > 1:
			raise MultipleSubscriptionException(
				"This customer has multiple subscriptions. Use Customer.subscriptions "
				"to access them."
			)
		else:
			return subscriptions.first()