ttk.Style.element_create using incorrect tk.call syntax

[jmorgensen]

BPO	23978
Nosy	@terryjreedy, @roseman, @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 = 'https://github.com/serhiy-storchaka'
closed_at = None
created_at = <Date 2015-04-16.22:49:38.007>
labels = ['type-bug', 'expert-tkinter']
title = 'ttk.Style.element_create using incorrect tk.call syntax'
updated_at = <Date 2015-08-06.21:25:09.278>
user = 'https://bugs.python.org/jmorgensen'

bugs.python.org fields:

activity = <Date 2015-08-06.21:25:09.278>
actor = 'terry.reedy'
assignee = 'serhiy.storchaka'
closed = False
closed_date = None
closer = None
components = ['Tkinter']
creation = <Date 2015-04-16.22:49:38.007>
creator = 'jmorgensen'
dependencies = []
files = []
hgrepos = []
issue_num = 23978
keywords = []
message_count = 3.0
messages = ['241286', '241370', '248149']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'markroseman', 'serhiy.storchaka', 'jmorgensen']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23978'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5', 'Python 3.6']

Linked PRs

• gh-68166: Add support of "vsapi" in ttk.Style.element_create() #111393
• gh-68166: Tkinter: Add tests and examples for element_create() #111453
• [3.12] gh-68166: Tkinter: Add tests and examples for element_create() (GH-111453) #111857
• [3.11] gh-68166: Tkinter: Add tests and examples for element_create() (GH-111453) #111858

[jmorgensen]

Style.element_create passes all spec elements as a single string into tk.call rather than breaking up arguments into "words." However, it passes the options properly as a list.

This causes python to crash with a stacktrace like the one below.

def element_create(self, elementname, etype, *args, **kw):
"""Create a new element in the current theme of given etype."""
    spec, opts = _format_elemcreate(etype, False, *args, **kw)
    self.tk.call(self._name, "element", "create", elementname, etype,
        spec, *opts)

And in _format_elemcreate:

    spec = "%s %s" % (iname, imagespec)
    ...
    spec = "%s %s %s" % (class_name, part_id, statemap)

Reproduction (on win):

>>> import ttk
>>> Style().element_create('custom.test', 'vsapi', 'SPIN', 2)
  File "<stdin>", line 1, in <module>
  File "C:\Miniconda\lib\lib-tk\ttk.py", line 466, in element_create
    spec, *opts)
_tkinter.TclError: missing required arguments 'class' and/or 'partId'

and, similarly:

>>> import ttk
>>> ttk.Style().element_create('custom.test', 'vsapi', 'SPIN', 2, width=5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Miniconda\lib\lib-tk\ttk.py", line 466, in element_create
    spec, *opts)
_tkinter.TclError: expected integer but got "-width"

[terryjreedy]

Reproduced on Win7, 3.4.3, with updated import: "from tkinter import ttk". The example should serve as a test.

[terryjreedy]

This looks like it should be an easy for for someone who understands tcl.call syntax. When we add ttk to Idle, I do not expect to use element_create, but maybe someone will want to to create a custom theme.

[serhiy-storchaka]

There are two ways to create new elements in Tkinter. One is by calling the elemnt_create() methods, and the other one by calling the theme_create() or theme_settings() method and using the elemnt_create key in the settings dict. In the former case it calls the ttk:style element create command directly, in the latter case it formats a script containing the ttk:style element create command and passes it as argument to the ttk:style theme create or the ttk:style theme settings command. There are enough differences between these two paths, so I expected that at least the latter works correctly. But it turned out that both ways do not work and never worked since adding this code in the stdlib. So it makes sense to consider it as a new feature rather than a bugfix. It should be documented correspondingly, and older versions should be made to raise more explicit exception when try to use the "vsapi" factory.

It is also an opportunity to change the Python API (which never worked) to closer match the Tk API. I.e. instead of

        style.element_create('pin', 'vsapi', 'EXPLORERBAR', 3,
                             ('pressed', '!selected', 3),
                             ('active', '!selected', 2),
                             ('pressed', 'selected', 6),
                             ('active', 'selected', 5),
                             ('selected', 4),
                             ('', 1))

it should be

        style.element_create('pin', 'vsapi', 'EXPLORERBAR', 3, [
                             ('pressed', '!selected', 3),
                             ('active', '!selected', 2),
                             ('pressed', 'selected', 6),
                             ('active', 'selected', 5),
                             ('selected', 4),
                             ('', 1)])

or

        style.element_create('pin', 'vsapi', 'EXPLORERBAR', 3, [
                             (('pressed', '!selected'), 3),
                             (('active', '!selected'), 2),
                             (('pressed', 'selected'), 6),
                             (('active', 'selected'), 5),
                             (('selected',), 4),
                             ((), 1)])

or

        style.element_create('pin', 'vsapi', 'EXPLORERBAR', 3, {
                             ('pressed', '!selected'): 3,
                             ('active', '!selected'): 2,
                             ('pressed', 'selected'): 6,
                             ('active', 'selected'): 5,
                             ('selected',): 4,
                             (): 1})