Issue #25523: Correct "a" article to "an" article
This changes the main documentation, doc strings, source code comments, and a
couple error messages in the test suite. In some cases the word was removed
or edited some other way to fix the grammar.
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 45c31a5..44116d8 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -75,7 +75,7 @@
"Another IOBase subclass, TextIOBase, deals with the encoding and decoding\n"
"of streams into text. TextIOWrapper, which extends it, is a buffered text\n"
"interface to a buffered raw stream (`BufferedIOBase`). Finally, StringIO\n"
-"is a in-memory stream for text.\n"
+"is an in-memory stream for text.\n"
"\n"
"Argument names are not part of the specification, and only the arguments\n"
"of open() are intended to be used as keyword arguments.\n"