Problem: Appropriate hash function not used.

Solution: use `hash()` function instead of `int.from_bytes()`

bigchaindb/common/memoize.py

@@ -5,7 +5,7 @@ from functools import lru_cache
 
 class HDict(dict):
     def __hash__(self):
-        return  int.from_bytes(codecs.decode(self['id'], 'hex'), 'big')
+        return hash(codecs.decode(self['id'], 'hex'))
 
 
 @lru_cache(maxsize=16384)
@@ -17,9 +17,9 @@ def memoize_from_dict(func):
 
     @functools.wraps(func)
     def memoized_func(*args, **kwargs):
-        print(args)
-        new_args = (args[0], HDict(args[1]), args[2])
-        print(new_args)
+        args = list(args)
+        args[1] = HDict(args[1])
+        new_args = tuple(args)
         return from_dict(func, *new_args, **kwargs)
 
     return memoized_func

bigchaindb/lib.py

@@ -77,10 +77,11 @@ class BigchainDB(object):
             raise ValidationError('Mode must be one of the following {}.'
                                   .format(', '.join(self.mode_list)))
 
+        tx_dict = transaction.tx_dict if transaction.tx_dict else transaction.to_dict()
         payload = {
             'method': mode,
             'jsonrpc': '2.0',
-            'params': [encode_transaction(transaction.to_dict())],
+            'params': [encode_transaction(tx_dict)],
             'id': str(uuid4())
         }
         # TODO: handle connection errors!

tests/conftest.py

@@ -256,7 +256,8 @@ def b():
 def create_tx(alice, user_pk):
     from bigchaindb.models import Transaction
     name = f'I am created by the create_tx fixture. My random identifier is {random.random()}.'
-    return Transaction.create([alice.public_key], [([user_pk], 1)], asset={'name': name})
+    return Transaction.create([alice.public_key], [([user_pk], 1)], asset={'name': name})\
+                      .sign([alice.private_key])
 
 
 @pytest.fixture