Add IANA character set aliases to the encodings alias dictionary

and make alias lookup lazy.

Note that only those IANA character set aliases were added for which
we actually have codecs in the encodings package.

Lib/encodings/__init__.py

@@ -4,8 +4,8 @@
     directory.
 
     Codec modules must have names corresponding to standard lower-case
-    encoding names with hyphens mapped to underscores, e.g. 'utf-8' is
-    implemented by the module 'utf_8.py'.
+    encoding names with hyphens and periods mapped to underscores,
+    e.g. 'utf-8' is implemented by the module 'utf_8.py'.
 
     Each codec module must export the following interface:
 
@@ -28,10 +28,11 @@ Written by Marc-Andre Lemburg (mal@lemburg.com).
 
 """#"
 
-import codecs,aliases,exceptions
+import codecs,exceptions
 
 _cache = {}
 _unknown = '--unknown--'
+_import_tail = ['*']
 
 class CodecRegistryError(exceptions.LookupError,
                          exceptions.SystemError):
@@ -40,19 +41,37 @@ class CodecRegistryError(exceptions.LookupError,
 def search_function(encoding):
     
     # Cache lookup
-    entry = _cache.get(encoding,_unknown)
+    entry = _cache.get(encoding, _unknown)
     if entry is not _unknown:
         return entry
 
-    # Import the module
+    # Import the module:
+    #
+    # First look in the encodings package, then try to lookup the
+    # encoding in the aliases mapping and retry the import using the
+    # default import module lookup scheme with the alias name.
+    #
     modname = encoding.replace('-', '_')
-    modname = aliases.aliases.get(modname,modname)
+    modname = modname.replace('.', '_')
     try:
-        mod = __import__(modname,globals(),locals(),'*')
+        mod = __import__('encodings.' + modname,
+                         globals(), locals(), _import_tail)
     except ImportError,why:
+        import aliases
+        modname = aliases.aliases.get(modname, _unknown)
+        if modname is not _unknown:
+            try:
+                mod = __import__(modname,
+                                 globals(), locals(), _import_tail)
+            except ImportError,why:
+                mod = None
+        else:
+            mod = None
+    if mod is None:
         # cache misses
         _cache[encoding] = None
         return None
+        
     
     # Now ask the module for the registry entry
     try:
@@ -79,6 +98,7 @@ def search_function(encoding):
     except AttributeError:
         pass
     else:
+        import aliases
         for alias in codecaliases:
             if not aliases.aliases.has_key(alias):
                 aliases.aliases[alias] = modname