No f-string in logging.basicConfig()

[shubham25powertech]

BPO	41782
Nosy	@vsajip, @ericvsmith

^{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 2020-09-14.15:09:14.722>
created_at = <Date 2020-09-14.13:49:54.225>
labels = ['invalid', 'type-feature', '3.8']
title = 'No f-string in logging.basicConfig()'
updated_at = <Date 2020-09-14.15:17:44.380>
user = 'https://bugs.python.org/shubham25powertech'

bugs.python.org fields:

activity = <Date 2020-09-14.15:17:44.380>
actor = 'eric.smith'
assignee = 'none'
closed = True
closed_date = <Date 2020-09-14.15:09:14.722>
closer = 'vinay.sajip'
components = []
creation = <Date 2020-09-14.13:49:54.225>
creator = 'shubham.25powertech'
dependencies = []
files = []
hgrepos = []
issue_num = 41782
keywords = []
message_count = 4.0
messages = ['376878', '376879', '376880', '376881']
nosy_count = 3.0
nosy_names = ['vinay.sajip', 'eric.smith', 'shubham.25powertech']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41782'
versions = ['Python 3.8']

[shubham25powertech]

There is no method to implement format strings in the basicConfig() method of the logging module. There are the implementations of '%', '{' or '$' for printf-style, str.format() or string.Template respectively using the style keyword.

[ericvsmith]

Since an f-string just evaluates to a regular string at the call site, before any logging code is invoked, there's nothing for the logging code to do. As far as it's concerned, it just gets a regular string.

[vsajip]

It's as Eric said. So I'll close this issue as "not a bug". An additional point - by using f-strings, you may be doing unnecessary string formatting - e.g. if the event doesn't actually get handled because of logger or handler level or filter settings. It's worse if any of the parameters in the f-string are expensive to compute, as they would effectively be thrown away if the event were not to be handled.

[ericvsmith]

Vinay raises a good point about performance that's well worth being aware of, especially with expensive objects (as he says). But since f-strings are much faster than other formatting (and especially .format()), there's a tradeoff. If I have something that I know is likely to be logged, sometimes I'll format it with f-strings.