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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 api_retrieve(self, api_key=None):
 		""" 		Call the stripe API's retrieve operation for this model. 		:param api_key: The api key to use for this request. Defaults to settings.STRIPE_SECRET_KEY. 		:type api_key: string 		"""

		api_key = api_key or self.default_api_key

		return self.stripe_class.retrieve(
			id=self.id, api_key=api_key, expand=self.expand_fields
		)