Moved the encoding map building logic from the individual mapping

codec files to codecs.py and added logic so that multi mappings
in the decoding maps now result in mappings to None (undefined mapping)
in the encoding maps.

55 files changed, 75 insertions, 162 deletions

diff --git a/Lib/codecs.py b/Lib/codecs.py
index b2eab1db3a..bdc8d029da 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__':
diff --git a/Lib/encodings/cp037.py b/Lib/encodings/cp037.py
index 5868372b07..3b641bb0e9 100644
--- a/Lib/encodings/cp037.py
+++ b/Lib/encodings/cp037.py
@@ -277,6 +277,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1006.py b/Lib/encodings/cp1006.py
index 593fbb601c..0a3c3af321 100644
--- a/Lib/encodings/cp1006.py
+++ b/Lib/encodings/cp1006.py
@@ -135,6 +135,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1026.py b/Lib/encodings/cp1026.py
index 3796a75c09..cce5af6a4a 100644
--- a/Lib/encodings/cp1026.py
+++ b/Lib/encodings/cp1026.py
@@ -277,6 +277,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1250.py b/Lib/encodings/cp1250.py
index 03a3e3177d..39cbc3375d 100644
--- a/Lib/encodings/cp1250.py
+++ b/Lib/encodings/cp1250.py
@@ -120,6 +120,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1251.py b/Lib/encodings/cp1251.py
index e27a122c38..4d4b6ee9b4 100644
--- a/Lib/encodings/cp1251.py
+++ b/Lib/encodings/cp1251.py
@@ -154,6 +154,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1252.py b/Lib/encodings/cp1252.py
index 5d7bdd6396..647f907287 100644
--- a/Lib/encodings/cp1252.py
+++ b/Lib/encodings/cp1252.py
@@ -73,6 +73,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1253.py b/Lib/encodings/cp1253.py
index abc144cc04..bfb4723b58 100644
--- a/Lib/encodings/cp1253.py
+++ b/Lib/encodings/cp1253.py
@@ -148,6 +148,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1254.py b/Lib/encodings/cp1254.py
index 4a2ab3caf4..dc662ed243 100644
--- a/Lib/encodings/cp1254.py
+++ b/Lib/encodings/cp1254.py
@@ -79,6 +79,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1255.py b/Lib/encodings/cp1255.py
index c987b85f45..6f70654f61 100644
--- a/Lib/encodings/cp1255.py
+++ b/Lib/encodings/cp1255.py
@@ -140,6 +140,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1256.py b/Lib/encodings/cp1256.py
index d72c5bcc9b..40ed577a85 100644
--- a/Lib/encodings/cp1256.py
+++ b/Lib/encodings/cp1256.py
@@ -126,6 +126,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1257.py b/Lib/encodings/cp1257.py
index d17a904217..baaf367b51 100644
--- a/Lib/encodings/cp1257.py
+++ b/Lib/encodings/cp1257.py
@@ -128,6 +128,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp1258.py b/Lib/encodings/cp1258.py
index 597f12438c..9a2827dc18 100644
--- a/Lib/encodings/cp1258.py
+++ b/Lib/encodings/cp1258.py
@@ -87,6 +87,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp424.py b/Lib/encodings/cp424.py
index bc10379808..4689996d66 100644
--- a/Lib/encodings/cp424.py
+++ b/Lib/encodings/cp424.py
@@ -277,6 +277,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp437.py b/Lib/encodings/cp437.py
index db1b88a567..a55e4246d9 100644
--- a/Lib/encodings/cp437.py
+++ b/Lib/encodings/cp437.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp500.py b/Lib/encodings/cp500.py
index 1c8fb57e17..bc1acde472 100644
--- a/Lib/encodings/cp500.py
+++ b/Lib/encodings/cp500.py
@@ -277,6 +277,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp737.py b/Lib/encodings/cp737.py
index 03665aea7d..6174d851a1 100644
--- a/Lib/encodings/cp737.py
+++ b/Lib/encodings/cp737.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp775.py b/Lib/encodings/cp775.py
index b38ccb5fe3..ee56f01f5b 100644
--- a/Lib/encodings/cp775.py
+++ b/Lib/encodings/cp775.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp850.py b/Lib/encodings/cp850.py
index e26287b7f3..dd2318721e 100644
--- a/Lib/encodings/cp850.py
+++ b/Lib/encodings/cp850.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp852.py b/Lib/encodings/cp852.py
index 431d8448f7..38df00f6fc 100644
--- a/Lib/encodings/cp852.py
+++ b/Lib/encodings/cp852.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp855.py b/Lib/encodings/cp855.py
index c9e71687bd..764fe1ac72 100644
--- a/Lib/encodings/cp855.py
+++ b/Lib/encodings/cp855.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp856.py b/Lib/encodings/cp856.py
index cc2e01f45a..9d09c09161 100644
--- a/Lib/encodings/cp856.py
+++ b/Lib/encodings/cp856.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp857.py b/Lib/encodings/cp857.py
index 6f4df23a56..5c84bb8318 100644
--- a/Lib/encodings/cp857.py
+++ b/Lib/encodings/cp857.py
@@ -168,6 +168,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp860.py b/Lib/encodings/cp860.py
index 057d91870f..a721ea3d46 100644
--- a/Lib/encodings/cp860.py
+++ b/Lib/encodings/cp860.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp861.py b/Lib/encodings/cp861.py
index 8db3b40b24..ccf26b70dc 100644
--- a/Lib/encodings/cp861.py
+++ b/Lib/encodings/cp861.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp862.py b/Lib/encodings/cp862.py
index 1cac3e278a..8f6d111e78 100644
--- a/Lib/encodings/cp862.py
+++ b/Lib/encodings/cp862.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp863.py b/Lib/encodings/cp863.py
index ecdc391f74..3596e645cc 100644
--- a/Lib/encodings/cp863.py
+++ b/Lib/encodings/cp863.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp864.py b/Lib/encodings/cp864.py
index 861fb00111..f510a269e8 100644
--- a/Lib/encodings/cp864.py
+++ b/Lib/encodings/cp864.py
@@ -167,6 +167,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp865.py b/Lib/encodings/cp865.py
index 4d9010df8f..cc4f719cb7 100644
--- a/Lib/encodings/cp865.py
+++ b/Lib/encodings/cp865.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp866.py b/Lib/encodings/cp866.py
index 6a8b0b0752..518eede0ad 100644
--- a/Lib/encodings/cp866.py
+++ b/Lib/encodings/cp866.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp869.py b/Lib/encodings/cp869.py
index 65d2b2e1d0..2e3ad35c1c 100644
--- a/Lib/encodings/cp869.py
+++ b/Lib/encodings/cp869.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp874.py b/Lib/encodings/cp874.py
index 31f4d3d6d4..c43e20be0f 100644
--- a/Lib/encodings/cp874.py
+++ b/Lib/encodings/cp874.py
@@ -168,6 +168,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/cp875.py b/Lib/encodings/cp875.py
index 3500446930..5e748734b5 100644
--- a/Lib/encodings/cp875.py
+++ b/Lib/encodings/cp875.py
@@ -278,6 +278,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_1.py b/Lib/encodings/iso8859_1.py
index f4c0bf750f..cea22611ac 100644
--- a/Lib/encodings/iso8859_1.py
+++ b/Lib/encodings/iso8859_1.py
@@ -41,6 +41,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_10.py b/Lib/encodings/iso8859_10.py
index c43c65306a..f29ebd237f 100644
--- a/Lib/encodings/iso8859_10.py
+++ b/Lib/encodings/iso8859_10.py
@@ -87,6 +87,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_13.py b/Lib/encodings/iso8859_13.py
index 2ab52927ec..e0c4ae4753 100644
--- a/Lib/encodings/iso8859_13.py
+++ b/Lib/encodings/iso8859_13.py
@@ -97,6 +97,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_14.py b/Lib/encodings/iso8859_14.py
index 5533e9617a..c84bb23e7f 100644
--- a/Lib/encodings/iso8859_14.py
+++ b/Lib/encodings/iso8859_14.py
@@ -72,6 +72,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_15.py b/Lib/encodings/iso8859_15.py
index 7bffff42b8..bf92acb291 100644
--- a/Lib/encodings/iso8859_15.py
+++ b/Lib/encodings/iso8859_15.py
@@ -49,6 +49,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_2.py b/Lib/encodings/iso8859_2.py
index 481f9a0a6c..1c92a54274 100644
--- a/Lib/encodings/iso8859_2.py
+++ b/Lib/encodings/iso8859_2.py
@@ -98,6 +98,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_3.py b/Lib/encodings/iso8859_3.py
index c2820ad6ad..ac8c8d91c2 100644
--- a/Lib/encodings/iso8859_3.py
+++ b/Lib/encodings/iso8859_3.py
@@ -76,6 +76,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_4.py b/Lib/encodings/iso8859_4.py
index 30d6ca6805..91db12613b 100644
--- a/Lib/encodings/iso8859_4.py
+++ b/Lib/encodings/iso8859_4.py
@@ -91,6 +91,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_5.py b/Lib/encodings/iso8859_5.py
index 2bdaa5003c..96cb0734f2 100644
--- a/Lib/encodings/iso8859_5.py
+++ b/Lib/encodings/iso8859_5.py
@@ -135,6 +135,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_6.py b/Lib/encodings/iso8859_6.py
index 585fa11e5d..298c2d53fe 100644
--- a/Lib/encodings/iso8859_6.py
+++ b/Lib/encodings/iso8859_6.py
@@ -134,6 +134,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_7.py b/Lib/encodings/iso8859_7.py
index 48f1bd58db..eea3abf2eb 100644
--- a/Lib/encodings/iso8859_7.py
+++ b/Lib/encodings/iso8859_7.py
@@ -121,6 +121,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_8.py b/Lib/encodings/iso8859_8.py
index a19aa671cc..45b2adac04 100644
--- a/Lib/encodings/iso8859_8.py
+++ b/Lib/encodings/iso8859_8.py
@@ -109,6 +109,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/iso8859_9.py b/Lib/encodings/iso8859_9.py
index a27890507a..ad0c19083d 100644
--- a/Lib/encodings/iso8859_9.py
+++ b/Lib/encodings/iso8859_9.py
@@ -47,6 +47,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/koi8_r.py b/Lib/encodings/koi8_r.py
index c28004ef6e..242d0c448a 100644
--- a/Lib/encodings/koi8_r.py
+++ b/Lib/encodings/koi8_r.py
@@ -169,6 +169,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/mac_cyrillic.py b/Lib/encodings/mac_cyrillic.py
index 45528319b2..6ae4a30e0e 100644
--- a/Lib/encodings/mac_cyrillic.py
+++ b/Lib/encodings/mac_cyrillic.py
@@ -164,6 +164,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/mac_greek.py b/Lib/encodings/mac_greek.py
index b7040c4bc4..839cf613c6 100644
--- a/Lib/encodings/mac_greek.py
+++ b/Lib/encodings/mac_greek.py
@@ -167,6 +167,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/mac_iceland.py b/Lib/encodings/mac_iceland.py
index f20e1344fb..284580cf9b 100644
--- a/Lib/encodings/mac_iceland.py
+++ b/Lib/encodings/mac_iceland.py
@@ -163,6 +163,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/mac_latin2.py b/Lib/encodings/mac_latin2.py
index 0fba502cd6..e922178177 100644
--- a/Lib/encodings/mac_latin2.py
+++ b/Lib/encodings/mac_latin2.py
@@ -167,6 +167,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/mac_roman.py b/Lib/encodings/mac_roman.py
index 6d048a3b6e..23dca89b41 100644
--- a/Lib/encodings/mac_roman.py
+++ b/Lib/encodings/mac_roman.py
@@ -164,6 +164,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/mac_turkish.py b/Lib/encodings/mac_turkish.py
index c81a864669..c71268b7ee 100644
--- a/Lib/encodings/mac_turkish.py
+++ b/Lib/encodings/mac_turkish.py
@@ -164,6 +164,4 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
diff --git a/Lib/encodings/rot_13.py b/Lib/encodings/rot_13.py
index 8c54811bb3..532ff646b7 100644
--- a/Lib/encodings/rot_13.py
+++ b/Lib/encodings/rot_13.py
@@ -93,9 +93,7 @@ decoding_map.update({
 
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
 
 ### Filter API
 
diff --git a/Tools/scripts/gencodec.py b/Tools/scripts/gencodec.py
index bc70a32309..69b6ede6c2 100644
--- a/Tools/scripts/gencodec.py
+++ b/Tools/scripts/gencodec.py
@@ -244,9 +244,7 @@ def getregentry():
     append('''
 ### Encoding Map
 
-encoding_map = {}
-for k,v in decoding_map.items():
-    encoding_map[v] = k
+encoding_map = codecs.make_encoding_map(decoding_map)
 ''')
     return string.join(l,'\n')