code: def vote_witness(self, witness, account=None):
          ''' Uses the steem_instance method to
          vote on a witness.
          '''
          if not account:
              account = self.mainaccount
          try:
              self.steem_instance().approve_witness(witness, account=account)
          except Exception as e:
              self.msg.error_message("COULD NOT VOTE " 
                                      + witness + " AS WITNESS: " + e)
              return False
          else:
              return Truf vote_witness(self, witness, account=None):
          ''' Uses the steem_instance method to
          vote on a witness.
          '''
          if not account:
              account = self.mainaccount
          try:
              self.steem_instance().approve_witness(witness, account=account)
          except Exception as e:
              self.msg.error_message("COULD NOT VOTE " 
                                      + witness + " AS WITNESS: " + e)
              return False
          else:
              return True
docs: Uses the steem_instance method to
          vote on a witness.