1 files changed, 21 insertions, 0 deletions
diff --git a/Lib/codecs.py b/Lib/codecs.py
index b2eab1d..bdc8d02 100644
--- a/Lib/codecs.py
+++ b/Lib/codecs.py
@@ -554,6 +554,27 @@ def make_identity_dict(rng):
         res[i]=i
     return res
 
+def make_encoding_map(decoding_map):
+
+    """ Creates an encoding map from a decoding map.
+
+        If a target mapping in the decoding map occurrs multiple
+        times, then that target is mapped to None (undefined mapping),
+        causing an exception when encountered by the charmap codec
+        during translation.
+
+        One example where this happens is cp875.py which decodes
+        multiple character to \u001a.
+
+    """
+    m = {}
+    for k,v in decoding_map.items():
+        if not m.has_key(v):
+            m[v] = k
+        else:
+            m[v] = None
+    return m
+    
 ### Tests
 
 if __name__ == '__main__':