logging.Formatter crashes when default_msec_format is None.

[felixxm]

BPO	40300
Nosy	@vsajip, @felixxm
PRs	bpo-40300: Allow empty logging.Formatter.default_msec_format. (GH-19551) #19551

^{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 2020-09-09.08:00:16.067>
created_at = <Date 2020-04-16.10:09:46.898>
labels = ['3.7', '3.8', 'type-feature', 'library', '3.9']
title = 'logging.Formatter crashes when default_msec_format is None.'
updated_at = <Date 2020-09-09.08:00:16.066>
user = 'https://github.com/felixxm'

bugs.python.org fields:

activity = <Date 2020-09-09.08:00:16.066>
actor = 'vinay.sajip'
assignee = 'none'
closed = True
closed_date = <Date 2020-09-09.08:00:16.067>
closer = 'vinay.sajip'
components = ['Library (Lib)']
creation = <Date 2020-04-16.10:09:46.898>
creator = 'felixxm'
dependencies = []
files = []
hgrepos = []
issue_num = 40300
keywords = ['patch']
message_count = 2.0
messages = ['366589', '366660']
nosy_count = 2.0
nosy_names = ['vinay.sajip', 'felixxm']
pr_nums = ['19551']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40300'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9']

[felixxm]

We would like to subclass logging.Formatter with a custom "default_time_format" and an empty "default_msec_format". Unfortunately logging.Formatter crashes when default_msec_format is None, see [1].

I'm happy to provide a patch.

[1]

cpython/Lib/logging/__init__.py

Line 607 in 5907e61

s = self.default_msec_format % (t, record.msecs)

[vsajip]

New changeset 06a3554 by Mariusz Felisiak in branch 'master':
bpo-40300: Allow empty logging.Formatter.default_msec_format. (GH-19551)
06a3554