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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 create_run_group(prj):
 """ Create a new 'run_group' in the database. This creates a new transaction in the database and creates a new run_group within this transaction. Afterwards we return both the transaction as well as the run_group itself. The user is responsible for committing it when the time comes. Args: prj - The project for which we open the run_group. Returns: A tuple (group, session) containing both the newly created run_group and the transaction object. """

    from benchbuild.utils import schema as s

    session = s.Session()
    experiment = prj.experiment
    group = s.RunGroup(id=prj.run_uuid, experiment=experiment.id)
    session.add(group)
    session.commit()

    return (group, session)