[3.10] bpo-43945: [Enum] reduce scope of new format() behavior (GH-26752)

* [Enum] reduce scope of new format behavior

Instead of treating all Enums the same for format(), only user mixed-in
enums will be affected.  In other words, IntEnum and IntFlag will not be
changing the format() behavior, due to the requirement that they be
drop-in replacements of existing integer constants.

If a user creates their own integer-based enum, then the new behavior
will apply:

    class Grades(int, Enum):
        A = 5
        B = 4
        C = 3
        D = 2
        F = 0

Now:  format(Grades.B)  -> DeprecationWarning and '4'
3.12:                   -> no warning, and 'B'.

(cherry picked from commit f60b07ab6c943fce084772c3c7731ab3bbd213ff)

Co-authored-by: Ethan Furman <ethan@stoneleaf.us>

1 files changed, 2 insertions, 2 deletions

diff --git a/Lib/asyncio/unix_events.py b/Lib/asyncio/unix_events.py
index a55b3a3..e4f445e 100644
--- a/Lib/asyncio/unix_events.py
+++ b/Lib/asyncio/unix_events.py
@@ -126,7 +126,7 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
                     logger.info('set_wakeup_fd(-1) failed: %s', nexc)
 
             if exc.errno == errno.EINVAL:
-                raise RuntimeError(f'sig {sig:d} cannot be caught')
+                raise RuntimeError(f'sig {sig} cannot be caught')
             else:
                 raise
 
@@ -160,7 +160,7 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
             signal.signal(sig, handler)
         except OSError as exc:
             if exc.errno == errno.EINVAL:
-                raise RuntimeError(f'sig {sig:d} cannot be caught')
+                raise RuntimeError(f'sig {sig} cannot be caught')
             else:
                 raise