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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, transaction=None):
 """Read the documents in this collection. This sends a ``RunQuery`` RPC and then returns an iterator which consumes each document returned in the stream of ``RunQueryResponse`` messages. .. note:: The underlying stream of responses will time out after the ``max_rpc_timeout_millis`` value set in the GAPIC client configuration for the ``RunQuery`` API. Snapshots not consumed from the iterator before that point will be lost. If a ``transaction`` is used and it already has write operations added, this method cannot be used (i.e. read-after-write is not allowed). Args: transaction (Optional[~.firestore_v1beta1.transaction.\ Transaction]):
 An existing transaction that the query will run in. Yields: ~.firestore_v1beta1.document.DocumentSnapshot: The next document that fulfills the query. """

        query = query_mod.Query(self)
        return query.stream(transaction=transaction)