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.

1 files changed, 1 insertions, 1 deletions

diff --git a/Lib/calendar.py b/Lib/calendar.py
index 02050ea457..5244b8d1ee 100644
--- a/Lib/calendar.py
+++ b/Lib/calendar.py
@@ -142,7 +142,7 @@ class Calendar(object):
 
     def iterweekdays(self):
         """
-        Return a iterator for one week of weekday numbers starting with the
+        Return an iterator for one week of weekday numbers starting with the
         configured first one.
         """
         for i in range(self.firstweekday, self.firstweekday + 7):