diff --git a/bigchaindb/common/transaction.py b/bigchaindb/common/transaction.py
index 3f59840f..b2c848d8 100644
--- a/bigchaindb/common/transaction.py
+++ b/bigchaindb/common/transaction.py
@@ -546,7 +546,7 @@ class Transaction(object):
         elif (operation == self.TRANSFER and
                 not (isinstance(asset, dict) and 'id' in asset)):
             raise TypeError(('`asset` must be a dict holding an `id` property '
-                             "for 'TRANSFER' Transactions"))
+                             "for \'TRANSFER\' Transactions"))
 
         if outputs and not isinstance(outputs, list):
             raise TypeError('`outputs` must be a list instance or None')
@@ -869,8 +869,9 @@ class Transaction(object):
             return cls._sign_threshold_signature_fulfillment(input_, message,
                                                              key_pairs)
         else:
-            raise ValueError("Fulfillment couldn't be matched to "
-                             'Cryptocondition fulfillment type.')
+            raise ValueError(
+                'Fulfillment couldn\'t be matched to '
+                'Cryptocondition fulfillment type.')
 
     @classmethod
     def _sign_simple_signature_fulfillment(cls, input_, message, key_pairs):
diff --git a/bigchaindb/core.py b/bigchaindb/core.py
index 87cc5819..4898ee94 100644
--- a/bigchaindb/core.py
+++ b/bigchaindb/core.py
@@ -46,9 +46,9 @@ class App(BaseApplication):
         self.chain = self.bigchaindb.get_latest_abci_chain()
 
     def log_abci_migration_error(self, chain_id, validators):
-        logger.error(f'An ABCI chain migration is in process. ' +
-                     'Download the new ABCI client and configure it with ' +
-                     'chain_id={chain_id} and validators={validators}.')
+        logger.error('An ABCI chain migration is in process. '
+                     'Download the new ABCI client and configure it with '
+                     f'chain_id={chain_id} and validators={validators}.')
 
     def abort_if_abci_chain_is_not_synced(self):
         if self.chain is None or self.chain['is_synced']:
@@ -69,8 +69,8 @@ class App(BaseApplication):
             chain_id = known_chain['chain_id']
 
             if known_chain['is_synced']:
-                msg = f'Got invalid InitChain ABCI request ({genesis}) - ' + \
-                      'the chain {chain_id} is already synced.'
+                msg = (f'Got invalid InitChain ABCI request ({genesis}) - '
+                       f'the chain {chain_id} is already synced.')
                 logger.error(msg)
                 sys.exit(1)
 
diff --git a/tests/backend/localmongodb/test_queries.py b/tests/backend/localmongodb/test_queries.py
index 1c587759..1d20854b 100644
--- a/tests/backend/localmongodb/test_queries.py
+++ b/tests/backend/localmongodb/test_queries.py
@@ -271,8 +271,8 @@ def test_get_spending_transactions_multiple_inputs():
         ({'transaction_id': tx3.id, 'output_index': 0}, 1, [tx4.id]),
         ({'transaction_id': tx3.id, 'output_index': 1}, 0, None),
     ]
-    for l, num, match in links:
-        txns = list(query.get_spending_transactions(conn, [l]))
+    for li, num, match in links:
+        txns = list(query.get_spending_transactions(conn, [li]))
         assert len(txns) == num
         if len(txns):
             assert [tx['id'] for tx in txns] == match