gh-69714: Make calendar module fully tested (#93655)

There are 3 paths to use `locale` argument in
`calendar.Locale{Text|HTML}Calendar.__init__(..., locale=None)`:
(1) `locale=None` -- denotes the "default locale"[1]
(2) `locale=""` -- denotes the native environment
(3) `locale=other_valid_locale` -- denotes a custom locale

So far case (2) is covered and case (1) is in 78935da (same branch).
This commit adds a remaining case (3).

[1] In the current implementation, this translates into the following
approach:

GET current locale
IF current locale == "C" THEN
  SET current locale TO ""
  GET current locale
ENDIF

* Remove unreachable code (and increase test coverage)

This condition cannot be true. `_locale.setlocale()` from the C module
raises `locale.Error` instead of returning `None` for
`different_locale.__enter__` (where `self.oldlocale` is set).

* Expand the try clause to calls to `LocaleTextCalendar.formatmonthname()`.

This method temporarily changes the current locale to the given locale,
so `_locale.setlocale()` may raise `local.Error`.


Co-authored-by: Rohit Mediratta <[email protected]>
Co-authored-by: Jessica McKellar <[email protected]>
Co-authored-by: Adam Turner <[email protected]>
Co-authored-by: Irit Katriel <[email protected]>

Lib/calendar.py

@@ -585,8 +585,6 @@ def __enter__(self):
         _locale.setlocale(_locale.LC_TIME, self.locale)
 
     def __exit__(self, *args):
-        if self.oldlocale is None:
-            return
         _locale.setlocale(_locale.LC_TIME, self.oldlocale)
 
 
@@ -690,7 +688,7 @@ def timegm(tuple):
     return seconds
 
 
-def main(args):
+def main(args=None):
     import argparse
     parser = argparse.ArgumentParser()
     textgroup = parser.add_argument_group('text only arguments')
@@ -747,7 +745,7 @@ def main(args):
         help="month number (1-12, text only)"
     )
 
-    options = parser.parse_args(args[1:])
+    options = parser.parse_args(args)
 
     if options.locale and not options.encoding:
         parser.error("if --locale is specified --encoding is required")
@@ -756,6 +754,9 @@ def main(args):
     locale = options.locale, options.encoding
 
     if options.type == "html":
+        if options.month:
+            parser.error("incorrect number of arguments")
+            sys.exit(1)
         if options.locale:
             cal = LocaleHTMLCalendar(locale=locale)
         else:
@@ -767,11 +768,8 @@ def main(args):
         write = sys.stdout.buffer.write
         if options.year is None:
             write(cal.formatyearpage(datetime.date.today().year, **optdict))
-        elif options.month is None:
-            write(cal.formatyearpage(options.year, **optdict))
         else:
-            parser.error("incorrect number of arguments")
-            sys.exit(1)
+            write(cal.formatyearpage(options.year, **optdict))
     else:
         if options.locale:
             cal = LocaleTextCalendar(locale=locale)
@@ -795,4 +793,4 @@ def main(args):
 
 
 if __name__ == "__main__":
-    main(sys.argv)
+    main()