Minor revision to the <BaseWidget._setup> method in Tkinter

[DrewFrench]

BPO	15303
Nosy	@ezio-melotti, @serhiy-storchaka
PRs	bpo-15303: Support widgets with boolean value False in Tkinter #23904
Files	tkbugfix.py: A revised version of the <BaseWidget._setup> method in Tkinter tkinter_widget_is_none.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 2020-12-25.19:48:59.890>
created_at = <Date 2012-07-09.08:25:49.856>
labels = ['type-feature', 'expert-tkinter', '3.10']
title = 'Minor revision to the <BaseWidget._setup> method in Tkinter'
updated_at = <Date 2020-12-25.19:48:59.889>
user = 'https://bugs.python.org/DrewFrench'

bugs.python.org fields:

activity = <Date 2020-12-25.19:48:59.889>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2020-12-25.19:48:59.890>
closer = 'serhiy.storchaka'
components = ['Tkinter']
creation = <Date 2012-07-09.08:25:49.856>
creator = 'Drew.French'
dependencies = []
files = ['26326', '28410']
hgrepos = []
issue_num = 15303
keywords = ['patch']
message_count = 5.0
messages = ['165070', '175233', '175236', '178007', '383746']
nosy_count = 4.0
nosy_names = ['gpolo', 'ezio.melotti', 'serhiy.storchaka', 'Drew.French']
pr_nums = ['23904']
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue15303'
versions = ['Python 3.10']

[DrewFrench]

In the <BaseWidget._setup> method, <master> is evaluated as a Boolean (when Tkinter attempts to find a parent for the widget). I think it should really be evaluated against <None>, seeing as that is the default <master> keyword argument value for most widgets. I ran into problems with this when making a container widget class that inherited from the <Canvas>, then implementing the <len> magic method. When the length was zero the widget would evaluate as false, which would prevented me from packing widgets inside my container widget.

I attached a revised version of the method.

[ezio-melotti]

Can you provide a patch in diff format?
You can find more information about how to do it on the devguide.

[gpolo]

Please include a short version of the widget class you mentioned. It must be only long enough to show the issue.

[serhiy-storchaka]

Here is a patch against 3.4 which contains proposed OP change and a lot of similar changes in different places. I'm not sure that this should be considered as a bug fix and not as an enhancement.

Drew, as a workaround you can implement __bool__() method which returns True for your widget. Or even better, do not make your container sequence-like.

[serhiy-storchaka]

New changeset bb70b2a by Serhiy Storchaka in branch 'master':
bpo-15303: Support widgets with boolean value False in Tkinter (GH-23904)
bb70b2a