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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 get_external_id(self, submission_id):
 """Returns human readable submission external ID. Args: submission_id: internal submission ID. Returns: human readable ID. """

    submission = self.find_by_id(submission_id)
    if not submission:
      return None
    if 'team_id' in submission.participant_id:
      return submission.participant_id['team_id']
    elif 'baseline_id' in submission.participant_id:
      return 'baseline_' + submission.participant_id['baseline_id']
    else:
      return ''