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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 check_subscription(self, request):
 		"""Redirect to the subscribe page if the user lacks an active subscription."""

		subscriber = subscriber_request_callback(request)

		if not subscriber_has_active_subscription(subscriber):
			if not SUBSCRIPTION_REDIRECT:
				raise ImproperlyConfigured("DJSTRIPE_SUBSCRIPTION_REDIRECT is not set.")
			return redirect(SUBSCRIPTION_REDIRECT)