Index: wflow-py/wflow/wflow_lib.py
===================================================================
diff -u -ra8927febfc0e3f567b5f5dddff0cb6ef139ad8e7 -r4efaa4c2e535431943e073dca2c8a31a334f8a77
--- wflow-py/wflow/wflow_lib.py	(.../wflow_lib.py)	(revision a8927febfc0e3f567b5f5dddff0cb6ef139ad8e7)
+++ wflow-py/wflow/wflow_lib.py	(.../wflow_lib.py)	(revision 4efaa4c2e535431943e073dca2c8a31a334f8a77)
@@ -51,6 +51,23 @@
 import gzip, zipfile
 
 
+
+def sum_list_cover(list_of_maps, covermap):
+    """
+    Sums a list of pcrastermap using cover to fill in missing values
+
+    :param list_of_maps: list of maps to sum
+    :param covermap: maps/ value to use fro cover
+
+    :return: sum of list of maps (single map)
+    """
+    sum_ = cover(0.0)
+    for map in list_of_maps:
+        sum_ = sum_ + cover(map,covermap)
+
+    return sum_
+
+
 def idtoid(sourceidmap, targetidmap,valuemap):
     """
     tranfer the values from valuemap at the point id's in sourceidmap to the areas in targetidmap.