diff --git a/install/test_balsam_hworld.py b/install/test_balsam_hworld.py
index 444b03c90..79f1bfbac 100644
--- a/install/test_balsam_hworld.py
+++ b/install/test_balsam_hworld.py
@@ -25,7 +25,7 @@ def wait_for_job_dir(basedb):
         time.sleep(1)
         sleeptime += 1
 
-    print('Waiting for Job Directory'.format(sleeptime))
+    print('Waiting for Job Directory {}'.format(sleeptime))
     while len(os.listdir(basedb)) == 0 and sleeptime < 15:
         print(sleeptime, end=" ", flush=True)
         time.sleep(1)
diff --git a/libensemble/history.py b/libensemble/history.py
index 3fbd80ef5..e5bacd2c6 100644
--- a/libensemble/history.py
+++ b/libensemble/history.py
@@ -129,7 +129,7 @@ def update_history_x_out(self, q_inds, sim_worker):
         else:
             self.given_count += len(q_inds)
 
-    def update_history_x_in(self, gen_worker, O):
+    def update_history_x_in(self, gen_worker, D):
         """
         Updates the history (in place) when new points have been returned from a gen
 
@@ -137,18 +137,18 @@ def update_history_x_in(self, gen_worker, O):
         ----------
         gen_worker: integer
             The worker who generated these points
-        O: numpy array
+        D: numpy array
             Output from gen_func
         """
 
-        if len(O) == 0:
+        if len(D) == 0:
             return
 
         rows_remaining = len(self.H)-self.index
 
-        if 'sim_id' not in O.dtype.names:
+        if 'sim_id' not in D.dtype.names:
             # gen method must not be adjusting sim_id, just append to self.H
-            num_new = len(O)
+            num_new = len(D)
 
             if num_new > rows_remaining:
                 self.grow_H(num_new-rows_remaining)
@@ -159,18 +159,18 @@ def update_history_x_in(self, gen_worker, O):
             # gen method is building sim_id or adjusting values in existing sim_id rows.
 
             # Ensure there aren't any gaps in the generated sim_id values:
-            assert np.all(np.in1d(np.arange(self.index, np.max(O['sim_id'])+1), O['sim_id'])),\
+            assert np.all(np.in1d(np.arange(self.index, np.max(D['sim_id'])+1), D['sim_id'])),\
                 "The generator function has produced sim_id that are not in order."
 
-            num_new = len(np.setdiff1d(O['sim_id'], self.H['sim_id']))
+            num_new = len(np.setdiff1d(D['sim_id'], self.H['sim_id']))
 
             if num_new > rows_remaining:
                 self.grow_H(num_new-rows_remaining)
 
-            update_inds = O['sim_id']
+            update_inds = D['sim_id']
 
-        for field in O.dtype.names:
-            self.H[field][update_inds] = O[field]
+        for field in D.dtype.names:
+            self.H[field][update_inds] = D[field]
 
         self.H['gen_time'][update_inds] = time.time()
         self.H['gen_worker'][update_inds] = gen_worker
diff --git a/libensemble/tools/gen_support.py b/libensemble/tools/gen_support.py
index 9e6604b60..344468f7b 100644
--- a/libensemble/tools/gen_support.py
+++ b/libensemble/tools/gen_support.py
@@ -1,17 +1,17 @@
 from libensemble.message_numbers import STOP_TAG, PERSIS_STOP, UNSET_TAG, EVAL_GEN_TAG
 
 
-def sendrecv_mgr_worker_msg(comm, O, status=None):
+def sendrecv_mgr_worker_msg(comm, output, status=None):
     """Send message from worker to manager and receive response.
     """
-    send_mgr_worker_msg(comm, O)
+    send_mgr_worker_msg(comm, output)
     return get_mgr_worker_msg(comm, status=status)
 
 
-def send_mgr_worker_msg(comm, O):
+def send_mgr_worker_msg(comm, output):
     """Send message from worker to manager.
     """
-    D = {'calc_out': O,
+    D = {'calc_out': output,
          'libE_info': {'persistent': True},
          'calc_status': UNSET_TAG,
          'calc_type': EVAL_GEN_TAG