code: def score_statement(self, st, extra_evidence=None):
          
          if extra_evidence is None:
              extra_evidence = []
          all_evidence = st.evidence + extra_evidence
          return self.score_evidence_list(all_evidence)
docs: Computes the prior belief probability for an INDRA Statement.
  
          The Statement is assumed to be de-duplicated. In other words,
          the Statement is assumed to have
          a list of Evidence objects that supports it. The prior probability of
          the Statement is calculated based on the number of Evidences it has
          and their sources.
  
          Parameters
          ----------
          st : indra.statements.Statement
              An INDRA Statements whose belief scores are to
              be calculated.
          extra_evidence : list[indra.statements.Evidence]
              A list of Evidences that are supporting the Statement (that aren't
              already included in the Statement's own evidence list.
  
          Returns
          -------
          belief_score : float
              The computed prior probability for the statement