[issue26177] tkinter: Canvas().keys returns empty strings.

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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resolution:  -> fixed
stage: commit review -> resolved
status: open -> closed

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[issue26177] tkinter: Canvas().keys returns empty strings.

[Roundup Robot]

Roundup Robot added the comment:

New changeset d86891dee68a by Serhiy Storchaka in branch '3.5':
Issue #26177: Fixed the keys() method for Canvas and Scrollbar widgets.
https://hg.python.org/cpython/rev/d86891dee68a

New changeset f0c895fb0374 by Serhiy Storchaka in branch '2.7':
Issue #26177: Fixed the keys() method for Canvas and Scrollbar widgets.
https://hg.python.org/cpython/rev/f0c895fb0374

New changeset 3a0bc2efed26 by Serhiy Storchaka in branch 'default':
Issue #26177: Fixed the keys() method for Canvas and Scrollbar widgets.
https://hg.python.org/cpython/rev/3a0bc2efed26

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[issue26177] tkinter: Canvas().keys returns empty strings.

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

> Is avoiding splitlist calls when not needed worthwhile?

We can't guarantee that future release of Tk wouldn't return a list of strings. 
Calling splitlist() for a tuple is cheap (but looks cumbersome).

> I am a bit curious why Canvas gives a different return.  Is the special 
> casing in _tkinter or tk itself?

Tk is full of such inconsistencies. A result for one widget can be a list of 
numbers, but for other it is a list of strings or a list of special Tcl 
objects. One method can return empty list, other returns empty string. One 
widgets truncate floating point parameters, others round them up or down.

I'll commit the patch after testing with Tk 8.5 and 8.4.

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[issue26177] tkinter: Canvas().keys returns empty strings.

[Terry J. Reedy]

Terry J. Reedy added the comment:

With patch applied to 3.5, tk.Canvas().keys() works and test_tk and other three 
files pass with -ugui.

Is avoiding splitlist calls when not needed worthwhile?  Tests also pass with 

def keys(self):
"""Return a list of all resource names of this widget."""
config = self.tk.call(self._w, 'configure')
if type(config) == tuple:
return [x[0][1:] for x in config]
else:  # str
splitlist = self.tk.splitlist
return [splitlist(x)[0][1:] for x in
splitlist(config)]

I am a bit curious why Canvas gives a different return.  Is the special casing 
in _tkinter or tk itself?  Otherwise, looks good to me.

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[issue26177] tkinter: Canvas().keys returns empty strings.

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

split() has many warts, it shouldn't be used. It is enough just call 
splitlist() for elements of a list.

Proposed patch fixes Misc.keys(). It also adds tests for missed options (some 
of them are not explicitly documented).

--
components: +Library (Lib), Tkinter
keywords: +patch
Added file: http://bugs.python.org/file41686/tkinter_keys.patch

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[issue26177] tkinter: Canvas().keys returns empty strings.

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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assignee:  -> serhiy.storchaka

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[issue26177] tkinter: Canvas().keys returns empty strings.

[Terry J. Reedy]

Terry J. Reedy added the comment:

Bug came from 
https://stackoverflow.com/questions/34911069/tk-canvas-options-keys-list-empy.  
Bryan Oakley answered that tk.Canvas().configure().keys() does work, making 
sorted(x.configure.keys()) a replacement for x.keys that should work for all 
widgets.

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[issue26177] tkinter: Canvas().keys returns empty strings.

[Terry J. Reedy]

New submission from Terry J. Reedy:

tkinter wraps tk widgets as option-value mappings with subscripting and 
.keys().  The latter does not work for Canvas (subscripting does).  First 
tested with 3.5.1, Win 10. First Text versus Canvas contrast below was 
confirmed with 2.7.11.

>>> import tkinter as tk
>>> tk.Text().keys()
['autoseparators', 'background', 'bd', 'bg', 'blockcursor', 'tabstyle', 
...
'takefocus', 'undo', 'width', 'wrap', 'xscrollcommand', 'yscrollcommand']
>>> tk.Canvas().keys()
['', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', 
'', '', '', '', '', '', '', '', '', '']

Explanation: Widget classes inherit keys from Misc via BaseWidget and Widget.  
Misc.keys calls into tk.

def keys(self):
"""Return a list of all resource names of this widget."""
return [x[0][1:] for x in
self.tk.splitlist(self.tk.call(self._w, 'configure'))]

The call returns different types for Text and Canvas.

>>> self = tk.Text()
>>> self.tk.call(self._w, 'configure')  # tuple of tuples
(('-autoseparators', 'autoSeparators', 'AutoSeparators', 1, 1),
 ('-background', 'background', 'Background', , 
'SystemWindow'), )
>>> self = tk.Canvas()
>>> self.tk.call(self._w, 'configure')  # tcl list as single string
'{-background background Background SystemButtonFace SystemButtonFace} {-bd 
borderWidth} {-bg background} {-borderwidth borderWidth BorderWidth 0 0} ...'

This difference between widgets seems odd.  A bug in tcl/tk/_tkinter?

tk.splitlist appears to return the Text tuple of tuples as is.  It splits the 
Canvas string into a tuple of strings

('-background background Background SystemButtonFace SystemButtonFace', '-bd 
borderWidth', ... )

but does not split the inner strings.  As a consequence, x[0] is the first 
character of each string ('{' as it turns out, though not relevant) and the 
slice [1:] of a single char string is always ''.

Possible remedy: tk.split also leaves tuple of tuples alone *and* splits the 
inner strings to a tuple.

>>> self.tk.split(self.tk.call(self._w, 'configure'))
(('-background', 'background', 'Background', 'SystemButtonFace', 'red'), 
('-bd', 'borderWidth'), ...)

So a fix (if the different returns are not changed) is to change 'splitlines' 
to 'split'.  With this change, keys (extracted as a function) gives the 
expected list.

>>> keys(tk.Canvas())
['background', 'bd', ..., 'yscrollincrement']

A test for Canvas().keys should be added somewhere.

--
messages: 258789
nosy: serhiy.storchaka, terry.reedy
priority: normal
severity: normal
stage: patch review
status: open
title: tkinter: Canvas().keys returns empty strings.
type: behavior
versions: Python 2.7, Python 3.5, Python 3.6

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