automated change using python-modernize: use 'as' in except

flask/debughelpers.py

@@ -76,7 +76,7 @@ def attach_enctype_error_multidict(request):
         def __getitem__(self, key):
             try:
                 return oldcls.__getitem__(self, key)
-            except KeyError, e:
+            except KeyError as e:
                 if key not in request.form:
                     raise
                 raise DebugFilesKeyError(request, key)