fix #73 : locking syntax error in Python 2.7

Author: mattsb42-aws

CHANGELOG.rst

@@ -7,8 +7,10 @@ Changelog
 
 Bugfixes
 --------
-* Fix ``MostRecentProvider`` behavior when lock cannot be acquired.
+* Fix :class:`MostRecentProvider` behavior when lock cannot be acquired.
   `#72 <https://github.com/awslabs/aws-dynamodb-encryption-python/issues/72>`_
+* Fix :class:`MostRecentProvider` lock acquisition for Python 2.7.
+  `#73 <https://github.com/awslabs/aws-dynamodb-encryption-python/issues/73>`_
 
 1.0.3 -- 2018-05-03
 ===================

src/dynamodb_encryption_sdk/material_providers/most_recent.py

@@ -240,7 +240,7 @@ def _get_most_recent_version(self, allow_local):
         :returns: version and corresponding cryptographic materials provider
         :rtype: CryptographicMaterialsProvider
         """
-        acquired = self._lock.acquire(blocking=not allow_local)
+        acquired = self._lock.acquire(not allow_local)
 
         if not acquired:
             # We failed to acquire the lock.