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
to fix the grammar.
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index d3cdbf1..633a6af 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -221,7 +221,7 @@
Even though :class:`IOBase` does not declare :meth:`read`, :meth:`readinto`,
or :meth:`write` because their signatures will vary, implementations and
clients should consider those methods part of the interface. Also,
- implementations may raise a :exc:`IOError` when operations they do not
+ implementations may raise an :exc:`IOError` when operations they do not
support are called.
The basic type used for binary data read from or written to a file is