Added an abstract base class so plugins don't need to add stubs for functions they don't care about.

bigchaindb/consensus/__init__.py

@@ -0,0 +1,43 @@
+# TODO: no real reason to use abc yet, but later we can enforce inheritance from
+#       this class when loading plugins if that's desirable.
+# from abc import ABCMeta
+
+class AbstractConsensusRules:
+
+    # TODO: rather than having plugin-authors inherit and override,
+    #       it'd be cleaner to make a `transactionrule` decorator and etc
+    @classmethod
+    def validate_transaction(cls, bigchain, transaction):
+        """Validate a transaction.
+
+        Args:
+            bigchain (Bigchain): an instantiated bigchaindb.Bigchain object.
+            transaction (dict): transaction to validate.
+
+        Returns:
+            The transaction if the transaction is valid else it raises an
+            exception describing the reason why the transaction is invalid.
+
+        Raises:
+            Descriptive exceptions indicating the reason the transaction failed.
+            See the `exceptions` module for bigchain-native error classes.
+        """
+        return transaction
+
+    @classmethod
+    def validate_block(cls, bigchain, block):
+        """Validate a block.
+
+        Args:
+            bigchain (Bigchain): an instantiated bigchaindb.Bigchain object.
+            block (dict): block to validate.
+
+        Returns:
+            The block if the block is valid else it raises and exception
+            describing the reason why the block is invalid.
+
+        Raises:
+            Descriptive exceptions indicating the reason the block failed.
+            See the `exceptions` module for bigchain-native error classes.
+        """
+        return block

bigchaindb/consensus/base.py

@@ -1,7 +1,8 @@
 import bigchaindb.exceptions as exceptions
 from bigchaindb.crypto import hash_data
+from bigchaindb.consensus import AbstractConsensusRules
 
-class ConsensusRules(object):
+class ConsensusRules(AbstractConsensusRules):
     """Base consensus rules for Bigchain.
 
     This class can be copied to write your own consensus rules!