Use dumb dbm driver for all platforms (#134)

* Use dumb dbm driver for all platforms
* Added py2.7 compatibility fallback

Author: nimnull

CHANGES.rst

@@ -1,5 +1,9 @@
-X.XX.X (YYYY MM DD)
-===================
+1.13.4 (2018 August 9)
+=====================
+
+Bugfixes
+--------
+* Enforce ``shelve`` to use ``dbm.dumb``/``dumbdbm`` modules for Python 3.x/2.7 respectively to prevent hiccups on a big amount of generated checkpoint. Was caught on macos X (``ndbm`` backend).
 
 Enhancements
 ------------

datarobot_batch_scoring/writer.py

@@ -17,6 +17,11 @@
     WriterQueueMsg, ProgressQueueMsg, REPORT_INTERVAL
 from datarobot_batch_scoring.utils import get_rusage
 
+if six.PY3:
+    import dbm.dumb as dumb_dbm
+else:
+    import dumbdbm as dumb_dbm
+
 
 class ShelveError(Exception):
     pass
@@ -83,7 +88,8 @@ def __enter__(self):
         assert(not self.is_open)
         self.is_open = True
         self._ui.debug('ENTER CALLED ON RUNCONTEXT')
-        self.db = shelve.open(self.file_context.file_name, writeback=True)
+        raw_db = dumb_dbm.open(self.file_context.file_name)
+        self.db = shelve.Shelf(raw_db, writeback=True)
         if not hasattr(self, 'partitions'):
             self.partitions = []
         return self