tkinter with wantobjects=False has been broken for some time

[gpolo]

BPO	3015
Nosy	@loewis, @asvetlov, @serhiy-storchaka
Files	tkinter_wantobjects.diff remove_wantobjects_internalRep.diff tkinter_deprecate_wantobjects.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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2016-10-24.20:53:40.142>
created_at = <Date 2008-05-30.22:51:37.199>
labels = ['type-bug', 'expert-tkinter']
title = 'tkinter with wantobjects=False has been broken for some time'
updated_at = <Date 2016-10-24.20:53:40.141>
user = 'https://bugs.python.org/gpolo'

bugs.python.org fields:

activity = <Date 2016-10-24.20:53:40.141>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2016-10-24.20:53:40.142>
closer = 'serhiy.storchaka'
components = ['Tkinter']
creation = <Date 2008-05-30.22:51:37.199>
creator = 'gpolo'
dependencies = []
files = ['10482', '10484', '31827']
hgrepos = []
issue_num = 3015
keywords = ['patch']
message_count = 16.0
messages = ['67562', '67567', '67575', '67577', '197767', '198167', '198168', '198169', '198170', '219012', '219171', '219177', '219247', '219267', '219268', '222813']
nosy_count = 8.0
nosy_names = ['loewis', 'gpolo', 'Arfrever', 'asvetlov', 'jesstess', 'python-dev', 'serhiy.storchaka', 'Lita.Cho']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue3015'
versions = ['Python 3.4']

[gpolo]

This affects only py3k, but apparently tkinter has been in this
situation for more than 9 months now.
I see these lines at _tkinter.c:

const char *s = Tcl_GetStringResult(self->interp);
const char *p = s;

res = PyUnicode_FromStringAndSize(s, (int)(p-s));

and I was wondering how could res not end up being an empty string
always ? Then I did some quick tests here and the return is always an
empty string, when wantobjects is set to False. Maybe the second line
should be:

const char *p = strchr(s, '\0');

I've attached this correction. Not sure if it is the best way to solve
the problem.

[loewis]

I think in Python 3, the whole wantobjects=False case should go. It was
a compatibility measure to support applications that didn't expect Tcl
objects; for Python 3, only a single case should be supported.

[gpolo]

I will agree that wantobjects=False should go, it is also discouraged to
use Tcl_GetStringResult because it may lose information.

But something should be done at FromObj since it accesses Tcl_Obj fields
directly, and it may end up not using the current object representation
which may cause weird things like in bpo-1447222. Said that, I'm not
sure how to fix it for now.

[gpolo]

I've removed wantobjects and substituted some internalRep usage too.

[serhiy-storchaka]

Looks as bpo-18877 is related to this. I have proposed for it a little different patch than first Guilherme's patch.

As for removing wantobjects, we perhaps can do this only in 3.4.

[python-dev]

New changeset 08c45e18e7b2 by Serhiy Storchaka in branch '3.3':
Issue bpo-3015: Fixed tkinter with wantobject=False. Any Tcl command call
http://hg.python.org/cpython/rev/08c45e18e7b2

New changeset 65dd0de6b4a5 by Serhiy Storchaka in branch 'default':
Issue bpo-3015: Fixed tkinter with wantobject=False. Any Tcl command call
http://hg.python.org/cpython/rev/65dd0de6b4a5

[serhiy-storchaka]

Here is a patch which change the default value for the wantobjects parameter of _tkinter.create() and adds deprecation warnings.

[Arfrever]

Here is a patch

You again forgot to attach a patch :) .

[serhiy-storchaka]

Oh, thanks Arfrever.

[LitaCho]

I am in the process of reviewing this patch, but I don't know what "wantobjects" does. I can make a guess, I think it is a hack to make tcl objects work in Python. I am guessing this is less needed in Python 3.4, but still has some dependencies.

If we can add in the documentation of what "wantobjects" is and why it is being depreciated somewhere, that would be great. I would do it myself, but I do need some direction.

I ran the tests, and it seems to run fine. The patch didn't have any new tests. We should add one that checks if the depreciation is working.

[jesstess]

@Lita.Cho: (I'd like to this on the web but the links are still broken after the website port) if you search for wantobjects in [Doc/whatsnew/2.3.rst](https://github.com/python/cpython/blob/main/Doc/whatsnew/2.3.rst), there's a description of why the parameter was added.

[serhiy-storchaka]

Now I think we shouldn't deprecate and remove wantobjects=False. Tkinter was partially broken with wantobjects=False, on other hand, it was partially broken with wantobjects=True. Many bugs was fixed last months, all tests now work with wantobjects=False, and I hope Tkinter now correctly supports both mode.

Besides using in old third-party code, this parameter is very helpful for testing. Tcl/Tk changes internal details from release to release, so when in one release Tk function returns list or integer, in other release it can return special object ('dict' or 'pixel'). Tkinter should be more stable against changing of return type, and wantobjects=False helps in detecting some such cases.

I propose to close this issue as fixed.