Corrections for a/an in code comments and documentation
diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index 80f3635..9d52fe1 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -909,7 +909,7 @@
 
 * an ISO 8859 codeset
 
-* a Microsoft Windows code page, which is typically derived from a 8859 codeset,
+* a Microsoft Windows code page, which is typically derived from an 8859 codeset,
   but replaces control characters with additional graphic characters
 
 * an IBM EBCDIC code page