syslog: Default "ident" in syslog.openlog() shouldn't contain slash

[vaclavbartos]

BPO	38361
Nosy	@miss-islington, @brandtbucher, @vaclavbartos
PRs	bpo-38361: syslog: fixed making default "ident" from sys.argv[0] #16557

^{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 2020-01-15.17:46:37.267>
created_at = <Date 2019-10-03.11:38:58.975>
labels = ['type-bug', 'library', '3.9']
title = 'syslog: Default "ident" in syslog.openlog() shouldn\'t contain slash'
updated_at = <Date 2020-01-15.17:46:37.244>
user = 'https://github.com/vaclavbartos'

bugs.python.org fields:

activity = <Date 2020-01-15.17:46:37.244>
actor = 'brandtbucher'
assignee = 'none'
closed = True
closed_date = <Date 2020-01-15.17:46:37.267>
closer = 'brandtbucher'
components = ['Library (Lib)']
creation = <Date 2019-10-03.11:38:58.975>
creator = 'vaclavbartos'
dependencies = []
files = []
hgrepos = []
issue_num = 38361
keywords = []
message_count = 2.0
messages = ['353839', '359984']
nosy_count = 3.0
nosy_names = ['miss-islington', 'brandtbucher', 'vaclavbartos']
pr_nums = ['16557']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38361'
versions = ['Python 3.9']

[vaclavbartos]

When syslog.openlog() is called without parameters (or syslog.syslog() is called directly), the ident parameter should be set to "sys.argv[0] with leading path components stripped" (citation from docs).

I suppose this means that when sys.argv[0] is "/some/path/to/script", the ident should be set to "script" (this is the behavior in Python 2.7)

However, in Python 3.x, it gets set to "/script", i.e. the last slash is included in the string. I suppose this is not intended, it is just a "one-off" error in parsing the string.

The fix is trivial, see the linked GitHub PR.

To reproduce the bug:

$ python3
>>> import sys
>>> import syslog
>>> sys.argv[0] = "/some/path/to/script"
>>> syslog.syslog("TEST MESSAGE")
>>> 
$ tail -n 1 /var/log/messages
Oct  3 11:11:46 localhost /script: TEST MESSAGE

[miss-islington]

New changeset f04750b by Miss Islington (bot) (Václav Bartoš) in branch 'master':
bpo-38361: syslog: fixed making default "ident" from sys.argv[0] (GH-16557)
f04750b