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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 stream(self, item, *, device_id=None, quality='hi', session_token=None):
 		"""Get MP3 stream of a podcast episode, library song, station_song, or store song. 		Note: 			Streaming requires a ``device_id`` from a valid, linked mobile device. 		Parameters: 			item (str):
 A podcast episode, library song, station_song, or store song. 				A Google Music subscription is required to stream store songs. 			device_id (str, Optional):
 A mobile device ID. 				Default: Use ``device_id`` of the :class:`MobileClient` instance. 			quality (str, Optional):
 Stream quality is one of ``'hi'`` (320Kbps), ``'med'`` (160Kbps), or ``'low'`` (128Kbps). 				Default: ``'hi'``. 			session_token (str):
 Session token from a station dict required for unsubscribed users to stream a station song. 				station['sessionToken'] as returend by :meth:`station` only exists for free accounts. 		Returns: 			bytes: An MP3 file. 		"""


		if device_id is None:
			device_id = self.device_id

		stream_url = self.stream_url(
			item,
			device_id=device_id,
			quality=quality,
			session_token=session_token
		)
		response = self.session.get(stream_url)
		audio = response.content

		return audio