code: def validate(self, bigchain, current_transactions=[]):
          
          input_conditions = []
  
          duplicates = any(txn for txn in current_transactions if txn.id == self.id)
          if bigchain.is_committed(self.id) or duplicates:
              raise DuplicateTransaction('transaction `{}` already exists'
                                         .format(self.id))
  
          if not self.inputs_valid(input_conditions):
              raise InvalidSignature('Transaction signature is invalid.')
  
          current_validators = self.get_validators(bigchain)
  
          # NOTE: Proposer should be a single node
          if len(self.inputs) != 1 or len(self.inputs[0].owners_before) != 1:
              raise MultipleInputsError('`tx_signers` must be a list instance of length one')
  
          # NOTE: Check if the proposer is a validator.
          [election_initiator_node_pub_key] = self.inputs[0].owners_before
          if election_initiator_node_pub_key not in current_validators.keys():
              raise InvalidProposer('Public key is not a part of the validator set')
  
          # NOTE: Check if all validators have been assigned votes equal to their voting power
          if not self.is_same_topology(current_validators, self.outputs):
              raise UnequalValidatorSet('Validator set much be exactly same to the outputs of election')
  
          return self
docs: Validate election transaction
  
          NOTE:
          * A valid election is initiated by an existing validator.
  
          * A valid election is one where voters are validators and votes are
            allocated according to the voting power of each validator node.
  
          Args:
              :param bigchain: (BigchainDB) an instantiated bigchaindb.lib.BigchainDB object.
              :param current_transactions: (list) A list of transactions to be validated along with the election
  
          Returns:
              Election: a Election object or an object of the derived Election subclass.
  
          Raises:
              ValidationError: If the election is invalid