Swap public and system ID in start_doctype_decl. Fixes #780300.
diff --git a/Lib/xml/sax/expatreader.py b/Lib/xml/sax/expatreader.py
index 58ad773..ab8cbc1 100644
--- a/Lib/xml/sax/expatreader.py
+++ b/Lib/xml/sax/expatreader.py
@@ -361,7 +361,7 @@
     def end_namespace_decl(self, prefix):
         self._cont_handler.endPrefixMapping(prefix)
 
-    def start_doctype_decl(self, name, pubid, sysid, has_internal_subset):
+    def start_doctype_decl(self, name, sysid, pubid, has_internal_subset):
         self._lex_handler_prop.startDTD(name, pubid, sysid)
 
     def unparsed_entity_decl(self, name, base, sysid, pubid, notation_name):