Add a new warnings.showwarnmsg() function taking a warnings.WarningMessage object

[vstinner]

BPO	26568
Nosy	@vstinner, @seberg
PRs	bpo-30812: Fix test_warnings, restore _showwarnmsg #2504 [3.6] bpo-30812: Fix test_warnings, restore _showwarnmsg (#2504) #2507
Files	warnings_showmsg.patch

^{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 2018-09-19.23:13:07.080>
created_at = <Date 2016-03-15.14:32:00.604>
labels = []
title = 'Add a new warnings.showwarnmsg() function taking a warnings.WarningMessage object'
updated_at = <Date 2018-09-19.23:13:07.079>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2018-09-19.23:13:07.079>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2018-09-19.23:13:07.080>
closer = 'vstinner'
components = []
creation = <Date 2016-03-15.14:32:00.604>
creator = 'vstinner'
dependencies = []
files = ['42172']
hgrepos = []
issue_num = 26568
keywords = ['patch']
message_count = 8.0
messages = ['261814', '261823', '262008', '262009', '262011', '278976', '297378', '297381']
nosy_count = 4.0
nosy_names = ['vstinner', 'THRlWiTi', 'python-dev', 'seberg']
pr_nums = ['2504', '2507']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue26568'
versions = ['Python 3.6']

[vstinner]

Currently, the warnings.showformat() function take between 4 and 6 parameters and it's not possible to add new parameters.

warnings.showformat() calls warnings.formatwarnings() with 5 parameters. Again, it's not easy to pass new parameters.

I would like to add a new "source" parameter for ResourceWarning: see issue bpo-26567 "ResourceWarning: Use tracemalloc to display the traceback where an object was allocated when a ResourceWarning is emitted".

To make warnings extensible, I propose to:

• Add new showmsg() and formatmsg() functions to the warnings module, these functions take a warnings.WarningMessage instance
• The _warnings module calls warnings.showmsg() rather than warnings.showwarning()
• For backward compatibility, warnings.showmsg() calls warnings.showwarning() if warnings.showwarning() was replaced. Same for warnings.formatmsg(): call warnings.formatwarning() if replaced.

Attached patch implements these changes.

With these changes, the warnings looks a little bit more like the logging module and its logging.LogRecord class.

The patch is incomplete, it doesn't add much tests yet and it doesn't touch the documentation. I would prefer to get the new API (and the whole idea) approved before going too far.

Note: If warnings.showwarning is deleted ("del warnings.showwarning"), showmsg() uses its own implementation. Same for formatmsg().

[vstinner]

I'm not sure about the method names showmsg() and formatmsg().

Maybe: showwarnmsg() and formatwarnmsg()?

First I used warnings.show() and warnings.format(), but "format()" is already the name of a builtin function.

By the way, I would prefer to use underscore between names, like show_msg() or show_warn_msg(). But I don't know if it's ok to use a different naming scheme in an existing module :-/

[python-dev]

New changeset 79888b970cc4 by Victor Stinner in branch 'default':
Add _showwarnmsg() and _formatwarnmsg() to warnings
https://hg.python.org/cpython/rev/79888b970cc4

[vstinner]

I pushed a change which adds a private _showwarnmsg(), but I'm still interested to make this new function public!

I pushed the change to unblock the issue bpo-26567.

[python-dev]

New changeset 9c92352324e8 by Victor Stinner in branch 'default':
Fix test_logging
https://hg.python.org/cpython/rev/9c92352324e8

[seberg]

To make warning testing saner, in numpy we added basically my own version of catch_warnings on steroids, which needed/will need changing because of this.

Unless I missed it somewhere, this change should maybe put into the release notes to warn make it a bit easier to track down what is going on.

[vstinner]

New changeset 7eebeb8 by Victor Stinner in branch 'master':
bpo-30812: Fix test_warnings, restore _showwarnmsg (bpo-2504)
7eebeb8

[vstinner]

New changeset d0aac5d by Victor Stinner in branch '3.6':
bpo-30812: Fix test_warnings, restore _showwarnmsg (bpo-2504) (bpo-2507)
d0aac5d