[issue32839] Add after_info as a function to tkinter

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Real use case for after_info() (with not arg): #33855 is about minimally 
testing all IDLE modules.  At least import the module and create class 
instances when easily possible.  For test_editor, I started with 

def test_init(self):  # Temporary.
e = Editor(root=self.root)
self.assertEqual(e.root, self.root)

and got in Shell

warning: callback failed in WindowList  : invalid 
command name ".!menu.windows"

and in the console

invalid command name "119640952recolorize"
while executing
"119640952recolorize"
("after" script)
invalid command name "119872312timer_event"
while executing
"119872312timer_event"
("after" script)
invalid command name "119872440config_timer_event"
while executing
"119872440config_timer_event"
("after" script)

Perhaps this is why I previously omitted something so obvious (it add 24% to 
coverage).

I added e._close(), which tries to cleanup, and the messages, in console only, 
are reduced to

bgerror failed to handle background error.
Original error: invalid command name "115211704timer_event"
Error in bgerror: can't invoke "tk" command: application has been destroyed
bgerror failed to handle background error.
Original error: invalid command name "115211832config_timer_event"
Error in bgerror: can't invoke "tk" command: application has been destroyed

I would like to know what _close misses, but it is hard to track them down.
print(self.root.tk.call('after', 'info')) after the close returned ('after#4', 
'after#3', 'after#1', 'after#0').  Adding

for id in cls.root.tk.call('after', 'info'):
self.root.after_cancel(id)

before cls.root.destroy() in shutDownClass stops the messages.
--

For test_del in #32831, I think the following might work, and be much shorter 
than the current code.

n = len(self.root.tk.call('after', 'info')
self.cc.__del__()
self.assertEqual(len(self.root.tk.call('after', 'info')), n-2)

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

Cheryl Sabella  added the comment:

A few questions about returning the Python function name (specifically, how to 
derive it).  This doesn't address the open issue with what to do about a Tcl 
command not tied to a Python function.

1.  Serhiy wrote "and the API for restoring the original Python callable is 
private."  What is that API?

2.  In the _register method, the Tcl command name is the callback ID + the 
function name:
f = CallWrapper(callback, None, self._root).__call__
cbname = repr(id(f))
try:
callback = callback.__func__
except AttributeError:
pass
try:
cbname = cbname + callback.__name__
except AttributeError:
pass 
So, with the values returned from tk.call('after', 'info', id) as (script, 
type), the Python function should be the same as script.lstrip('0123456789').  
I'm not sure if that would be the best way to get the name back.

3.  In tkinter, there is a list created/added to during _register:
self._tclCommands.append(cbname)
where cbname is the Tcl command name (as defined by the code in q2 above).  
Would it be possible to change _tclCommands to a dict mapping Tcl command name 
to Python function name?  _tclCommands already has some logic around it, 
including .remove functions, so I think a dictionary would be more efficient 
for the exisitng purposes.  Since it's semi-private, is there a fear with 
backward compatibility if it changes from a list to a dict?  Is it better to 
add a new dict variable?

Thanks!

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

Change by Cheryl Sabella :


--
dependencies: +tkinter after_cancel does not behave correctly when called with 
id=None

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

Cheryl Sabella  added the comment:

I created issue32857 for the after_cancel issue.  Thanks!

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[issue32839] Add after_info as a function to tkinter

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I agreed with Cheryl's conclusion that likely after_cancel() had been called 
with None. The comments about 8.4 is wrong, and the solution in issue763637 is 
not correct. The current code code deletes the script for the first event if 
pass None to after_cancel(). Do you ming to open a PR for proper solving 
issue763637 Cheryl?

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[issue32839] Add after_info as a function to tkinter

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

> Since events are removed from Tcl once that are invoked, how would the 
> dictionary be cleaned up?  Would after_info need to be polled every once in a 
> while to clean up the dictionary or would it just exist until the object is 
> destroyed?

Good question. Currently the reference to a callable is kept in the dict  until 
the object is destroyed. This can be considered as a bug (see issue1524639).

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[issue32839] Add after_info as a function to tkinter

[Terry J. Reedy]

Terry J. Reedy  added the comment:

A person who can create a tcl callback with tk.call can inquire with 
tk.call('after', 'info', id).  That does not cover callbacks created by tcl or 
extensions thereof, but references to such callbacks are unlikely to be useful 
to anyone who does not know any tcl.

I see these choices for after_info(id):

A. Return the tcl script reference even when it wraps a python function.  I 
don't like this, as the tcl reference is useless to most people.

B. Convert the reference to a Python function if possible but return it if not. 
 This is a bit awkward to document and any use requires a type check.  Having a 
function return such different types, depending on the input, is frowned upon.

C. Convert the reference to a function if possibe and raise TypeError or 
ValueError is not.  This is incomplete but easier for a pure Python programmer 
to deal with.  The documentation could specify how those who want a tcl 
reference can get it.

D. Don't implement after_info(id), at least not now, and just after_info().  
Information about the current existence of a callback is contained in the list 
returned by after_info().  Each of the following pairs should be equivalent:

  assertIn(id, after_info())
  assertEqual(len(after_info(id)), 2)

  assertNotIn(id, after_info())
  assertRaises(TclError, after_info, id)

(For testing after_info(), assertIn and assertNotIn avoid assuming that tcl 
does not add any internal callbacks.)

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

Cheryl Sabella  added the comment:

>>> It is internal, it was not exposed to Tkinter users before, and the API for 
>>> restoring the original Python callable is private.

I thought `bind(sequence)` also returned these internal Tcl function names?  
For example, if I do a print on the set_breakpoint_here text widget in IDLE, it 
prints :
if {"[140358823678376set_breakpoint_here %# %b %f %h %k %s %t %w %x %y %A %E %K 
%N %W %T %X %Y %D]" == "break"} break


In order for it to return the python function name, I think the `after` 
function would need to write to a dictionary of `name: func` where name is 
currently used as the Tcl function name that is registered?  Is there something 
in tkinter that does this now that it could be modeled from?  Since events are 
removed from Tcl once that are invoked, how would the dictionary be cleaned up? 
 Would after_info need to be polled every once in a while to clean up the 
dictionary or would it just exist until the object is destroyed?

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[issue32839] Add after_info as a function to tkinter

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Note that in the tests for issue32831 you need to use call('after', 'info') if 
you want to backport them.

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[issue32839] Add after_info as a function to tkinter

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

On one side, the first item of the list returned by the Tcl command `after info 
$id` is a name of the Tcl command generated by Tkinter. It is internal, it was 
not exposed to Tkinter users before, and the API for restoring the original 
Python callable is private.

On other side, `after info` can return not only events created by Tkinter, but 
events created by Tcl (either by direct execution of Tcl script, this is still 
can be useful with programming with Tkinter, or created by the Tcl standard 
library or third-party Tcl libraries). In that case a Python callable can't be 
returned.

This is what I was uncertain about. Maybe after_info() should return a Python 
callable if possible, and keep the original result otherwise? This complicates 
its implementation and definition.

TclError is legal and expected. In some methods it is caught, either because 
the method is purposed to be called at widget destroying stage, when the order 
of different cleanup procedures is not specified, and Tcl names can be 
destroyed before destroying Tkinter wrappers, or because the method was 
implemented differently in the past, and catching TclError is needed for 
backward compatibility. after_info() is not the case.

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[issue32839] Add after_info as a function to tkinter

[Terry J. Reedy]

Terry J. Reedy  added the comment:

I am in favor of exposing all of tk where it makes sense to do so, and I think 
it does here.

After 'translating' the tk after_info entry into tkinter-ese, I would expect 
and want that
  root.after_info(root.after(f, 10))[0] is f
be true.  the same as would be true of the tcl equivalent. (This could even be 
a test.)  It appears that the current patch instead returns a (python) 
reference to the tcl wrapper of f.  The fact that python callbacks get wrapped 
as tcl callbacks is currently transparent to tkinter users and should remain so.

Serhiy, I presume that this is what you were uncertain about.  I am presuming 
above that f can be recovered.

Returning the function kind as 'timer' or 'idle' is fine. In other contexts, an 
enumeration would be a possibility, but this does not seem to fit tkinter.

I presume a bad id results in TclError.  Do other tkinter functions allow 
TclError to propagate?  My impression is no.  If so, it should be replaced here 
in a way consistent with other tkinter practice.

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

Cheryl Sabella  added the comment:

I've made a pull request.  I understand that you may not want to add this 
functionality, but perhaps the docstring will answer your questions.  I took it 
from the Tcl docs page.

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

Change by Cheryl Sabella :


--
keywords: +patch
pull_requests: +5466
stage:  -> patch review

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[issue32839] Add after_info as a function to tkinter

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I'm not sure what after_info(id) should return.

--
nosy: +terry.reedy

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

Cheryl Sabella  added the comment:

I was working on the tests for issue32831.  One of the methods was `__del__` 
which made sure timer events were canceled with `after_cancel`.  In the test, 
to assert that the after events no longer existed after calling `__del__` and 
after reading the Tcl documentation for `after`, I tried to call `after_info` 
but it didn't exist. So I added a call to `self.tk.call('after', 'info', id)` 
directly to assert that the after events no longer existed.

I don't know if there is a general need to know whether timer or idle events 
exist, but this command gives that information.

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[issue32839] Add after_info as a function to tkinter

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

What is the use case for this method? How it could be used?

--
nosy: +serhiy.storchaka

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[issue32839] Add after_info as a function to tkinter

[Cheryl Sabella]

New submission from Cheryl Sabella :

In tkinter, after_cancel has a call to after info:
data = self.tk.call('after', 'info', id)

Since this is a supported command, there should be a function to access it 
directly.

https://www.tcl.tk/man/tcl8.6/TclCmd/after.htm

--
components: Tkinter
messages: 312119
nosy: csabella
priority: normal
severity: normal
status: open
title: Add after_info as a function to tkinter
type: enhancement
versions: Python 3.8

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