[clang.py] Followup to TranslationUnit refactor

* Document index argument in TranslationUnit.from_source
* Add numeric error code to TranslationUnitSaveError string representation
* Use None instead of [] for default argument value in

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156722 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/bindings/python/clang/cindex.py b/bindings/python/clang/cindex.py
index fa82294..0053796 100644
--- a/bindings/python/clang/cindex.py
+++ b/bindings/python/clang/cindex.py
@@ -126,7 +126,7 @@
                             "value supported." % enumeration)
         self.save_error = enumeration
-        Exception.__init__(self, message)
+        Exception.__init__(self, 'Error %d: %s' % (enumeration, message))
 ### Structures and Utility Classes ###
@@ -1739,6 +1739,9 @@
         options is a bitwise or of TranslationUnit.PARSE_XXX flags which will
         control parsing behavior.
+        index is an Index instance to utilize. If not provided, a new Index
+        will be created for this TranslationUnit.
         To parse source from the filesystem, the filename of the file to parse
         is specified by the filename argument. Or, filename could be None and
         the args list would contain the filename(s) to parse.
@@ -1925,7 +1928,7 @@
             raise TranslationUnitSaveError(result,
                 'Error saving TranslationUnit.')
-    def codeComplete(self, path, line, column, unsaved_files=[], options=0):
+    def codeComplete(self, path, line, column, unsaved_files=None, options=0):
         Code complete in this translation unit.