Replace another test of in dict_.keys() with a defaultdict, and simplify nearby code.

Author: JamesParrott

shapefile.py

@@ -9,6 +9,7 @@
 __version__ = "2.3.1"
 
 import array
+import collections
 import io
 import logging
 import os
@@ -393,12 +394,11 @@ def organize_polygon_rings(rings, return_errors=None):
             return polys
 
         # first determine each hole's candidate exteriors based on simple bbox contains test
-        hole_exteriors = dict([(hole_i, []) for hole_i in xrange(len(holes))])
-        exterior_bboxes = [ring_bbox(ring) for ring in exteriors]
-        for hole_i in hole_exteriors.keys():
+        hole_exteriors = collections.defaultdict(list)
+        for hole_i in xrange(len(holes)):
             hole_bbox = ring_bbox(holes[hole_i])
-            for ext_i, ext_bbox in enumerate(exterior_bboxes):
-                if bbox_contains(ext_bbox, hole_bbox):
+            for ext_i, ring in enumerate(exteriors):
+                if bbox_contains(ring_bbox(ring), hole_bbox):
                     hole_exteriors[hole_i].append(ext_i)
 
         # then, for holes with still more than one possible exterior, do more detailed hole-in-ring test