TimedRotatingFileHandler backupCount not working

[ivogrondman]

BPO	45628
Nosy	@vsajip, @miss-islington
PRs	bpo-45628: Check all parts of the suffix for an extension match. (GH-29310) #29310 [3.9] bpo-45628: Check all parts of the suffix for an extension match. (GH-29310) (GH-29313) #29313 [3.10] bpo-45628: Check all parts of the suffix for an extension match. (GH-29310) (GH-29314) #29314
Files	logrotate.py: Example script

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-10-29.15:27:27.359>
created_at = <Date 2021-10-27.15:23:13.131>
labels = ['library', '3.10']
title = 'TimedRotatingFileHandler backupCount not working'
updated_at = <Date 2022-01-28.23:18:45.219>
user = 'https://bugs.python.org/ivogrondman'

bugs.python.org fields:

activity = <Date 2022-01-28.23:18:45.219>
actor = 'brandtbucher'
assignee = 'none'
closed = True
closed_date = <Date 2021-10-29.15:27:27.359>
closer = 'vinay.sajip'
components = ['Library (Lib)']
creation = <Date 2021-10-27.15:23:13.131>
creator = 'ivogrondman'
dependencies = []
files = ['50397']
hgrepos = []
issue_num = 45628
keywords = ['patch']
message_count = 6.0
messages = ['405104', '405304', '405310', '405311', '405312', '405316']
nosy_count = 3.0
nosy_names = ['vinay.sajip', 'miss-islington', 'ivogrondman']
pr_nums = ['29310', '29313', '29314']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue45628'
versions = ['Python 3.10']

[ivogrondman]

Using the TimedRotatingFileHandler with a non-zero backupCount, I get different behaviour between versions 3.9 and 3.10.

Attached is a small example. Running it with 3.9 gives me two backups at most even if I run the script for a long time. Running it with 3.10 does not delete old backup files at all and just keeps writing new ones.

[vsajip]

New changeset 8a77f59 by Vinay Sajip in branch 'main':
bpo-45628: Check all parts of the suffix for an extension match. (GH-29310)
8a77f59

[vsajip]

New changeset 317e0c9 by Miss Islington (bot) in branch '3.9':
[3.9] bpo-45628: Check all parts of the suffix for an extension match. (GH-29310) (GH-29313)
317e0c9

[vsajip]

New changeset 191a939 by Miss Islington (bot) in branch '3.10':
[3.10] bpo-45628: Check all parts of the suffix for an extension match. (GH-29310) (GH-29314)
191a939

[vsajip]

N.B. I was able to reproduce this on recent 3.9 versions as well.

[vsajip]

It's possible this crept in during the fix for bpo-44753.