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skipitem() in getargs.c still supports 'w' and 'w#', and shouldn't #68114
Description
| BPO | 23926 |
|---|---|
| Nosy | @vstinner, @larryhastings, @serhiy-storchaka, @llllllllll |
| PRs | |
| Files |
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 = 'https://github.com/larryhastings'
closed_at = None
created_at = <Date 2015-04-13.02:44:00.845>
labels = ['interpreter-core', '3.8', 'type-bug', '3.7']
title = "skipitem() in getargs.c still supports 'w' and 'w#', and shouldn't"
updated_at = <Date 2018-07-09.16:05:58.680>
user = 'https://github.com/larryhastings'bugs.python.org fields:
activity = <Date 2018-07-09.16:05:58.680>
actor = 'llllllllll'
assignee = 'larry'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2015-04-13.02:44:00.845>
creator = 'larry'
dependencies = []
files = ['38972', '39931']
hgrepos = []
issue_num = 23926
keywords = ['patch']
message_count = 8.0
messages = ['240587', '240794', '246780', '247383', '253226', '263709', '263776', '321300']
nosy_count = 4.0
nosy_names = ['vstinner', 'larry', 'serhiy.storchaka', 'llllllllll']
pr_nums = ['8204']
priority = 'low'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23926'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']
Activity
larryhastings commentedon Apr 13, 2015
tl;dr: skipitem() in Python 3 still supports "w" and "w#", which were abandoned. They should be removed.
--
If:
PyArg_ParseTupleAndKeywords (or its cousins),
CPython will call skipitem() to skip over the remaining positional parameters so it can process keyword arguments. It does this by knowing all the format units, and iterating over them and throwing away the various varargs pointers until it hits the keyword arguments part of the format string.
PyArg_ParseTuple() etc. in Python 2 supported "w" and "w#" for parsing "objects with the read-write buffer interface". These were removed in Python 3.
skipitem() in Python 3 still supports both skipping "w" and "w#". But in fact the only legal format unit starting with a 'w' in Python 3 is 'w*'. So a function with a 'w*' as an optional parameter that got skipped would be misinterpreted; skipitem would see the 'w', not recognize the following '*' and leave it there, then the next function that read a character from the format string (either skipitem() or convertsimple()) would see the '*' and throw an "impossible <bad format char>" exception.
llllllllll commentedon Apr 13, 2015
here is a patch and test case.
I added an entry to Misc/NEWS. I tried to follow the format; however, let me know if I have done this incorrectly.
llllllllll commentedon Jul 15, 2015
Sorry it took so long to get back to this. I didn't realize this was still open. I have provided the update to the docs and moved it to the 3.6 section. I also made sure the patch still applies and the tests all pass.
llllllllll commentedon Jul 25, 2015
bumping so that we don't forget about this.
llllllllll commentedon Oct 20, 2015
bumping this issue
llllllllll commentedon Apr 19, 2016
bump
vstinner commentedon Apr 19, 2016
I reviewed skipitems.patch.
serhiy-storchaka commentedon Jul 9, 2018
Do you mind to convert your patch into a pull request Joe?
gh-68114: Fix handling for removed PyArg_ParseTuple 'w' formatters (GâĶ