warnings in interactive sessions

[malemburg]

BPO	1539925
Nosy	@malemburg, @birkenfeld, @ncoghlan, @vadmium, @serhiy-storchaka

^{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 = None
created_at = <Date 2006-08-14.11:03:41.000>
labels = ['3.7', 'type-feature', 'library']
title = 'warnings in interactive sessions'
updated_at = <Date 2017-11-14.01:01:29.867>
user = 'https://github.com/malemburg'

bugs.python.org fields:

activity = <Date 2017-11-14.01:01:29.867>
actor = 'ncoghlan'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2006-08-14.11:03:41.000>
creator = 'lemburg'
dependencies = []
files = []
hgrepos = []
issue_num = 1539925
keywords = []
message_count = 5.0
messages = ['60969', '85079', '199793', '306141', '306180']
nosy_count = 6.0
nosy_names = ['lemburg', 'georg.brandl', 'ncoghlan', 'martin.panter', 'serhiy.storchaka', 'Alan.Cristhian']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue1539925'
versions = ['Python 3.7']

[malemburg]

Carried over from Patch bpo-1538956 description:

During testing I found that the warning registry
defaults to only issueing warnings once per module and
line number.

I suppose this is enough for debugging code, but it
feels weird when trying things in the interactive
session, as you only get the warnings once in that
context (and for the whole session), regardless of the
fact that you're entering new lines of code all the time.

The reason is that the warning framework registers
warnings based on line number which usually is 1 in
interactive sessions.

In general, it might be a better idea to have a single
global warning registry and then include the module
name or id in the registry key. Currently, the warning
framework creates a new registry per (module) context.

[brettcannon]

Not a bad idea, although it would require some work to make it work in a
backwards-compatible fashion.

[birkenfeld]

Is there still any interest in this?

[serhiy-storchaka]

Looks reasonable to me. Perhaps we should port the solution from IPython:
ipython/ipython#6611.

[ncoghlan]

As a user, what would I actually gain from being warned more than once per session that a particular API I'm using is deprecated?

If I want that behaviour, I can already opt in to it by doing "warnings.simplefilter('always')".

As things stand, the perpetually reset line counter just means that the effective default at the REPL is "warnings.simplefilter('module:::main')"