'Validate the Block without validating the transactions.
Args:
bigchain (:class:`~bigchaindb.Bigchain`): An instantiated Bigchain
object.
Raises:
ValidationError: If there is a problem with the block'

def _validate_block(self, bigchain):

    if (self.node_pubkey not in bigchain.federation):
        raise SybilError('Only    federation    nodes    can    create    blocks')
    if (not self.is_signature_valid()):
        raise InvalidSignature('Invalid    block    signature')
    txids = [tx.id for tx in self.transactions]
    if (len(txids) != len(set(txids))):
        raise DuplicateTransaction('Block    has    duplicate    transaction')
