[Tcl-bugs] [ tktoolkit-Bugs-1851526 ] 8.5 breaks some Tkinter text widgets

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Bugs item #1851526, was opened at 2007-12-15 22:10
Message generated for change (Comment added) made by loewis
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Category: 18. [text]
Group: None
Status: Open
Resolution: None
Priority: 8
Private: No
Submitted By: George Peter Staplin (georgeps)
Assigned to: George Peter Staplin (georgeps)
Summary: 8.5 breaks some Tkinter text widgets

Initial Comment:
8.5 is causing the Tkinter EditorWindow class to break for some unknown reason.  When the user clicks <1> the event is delivered, but for some reason the Tk code isn't behaving properly.  Therefore you can't select text for copying and pasting.

This is this code that seems to break with 8.5, and I'm not sure why yet:
Python-2.5.1/Lib/idlelib/EditorWindow.py

The same code works fine with Python 2.5.1 using Tcl/Tk 8.4.

Here's what I've done so far:
I've verified that the events are being delivered with this code:
print(text.bind_class ("Text", "<1>", None, None)) 
cmd = text.bind_class("Text", "<1>", None, None)
cmd = 'puts TextB1;' + cmd
text.bind_class ("Text", "<1>", cmd)

I've gone hunting in various other places for the bug, with little success.

You can run: /path/to/8.5/using/python EditorWindow.py 

Whatever this bug is breaks IDLE (the standard Python editor that uses Tkinter).

In a related note: they are using MacOSX private symbols, so it may already be broken on Mac OS X if those are MODULE_SCOPEd. Some sort of better cooperation is needed between the Tkinter and Tk developers.

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Comment By: Martin v. Löwis (loewis)
Date: 2008-01-04 23:37

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re "fiddles with the intreps for performance stuff". It's not just for
performance, but also for correctness. While '100' and 100 are the same to
Tcl, they are not in Python. We had huge problems with fragility when Tcl
started using Unicode in some contexts; we really need to know it's a
Unicode string, or else we cannot know whether to convert it to a Python
byte string or a Unicode string.

re bgerror: Please trust me that "define a procedure that does what you
want" does not work. Just define

def bgerror(msg):
  raise TclError(msg)

and see for yourself.

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Comment By: Michael Schlenker (mic42)
Date: 2008-01-04 17:51

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Hi Loewis,

re: Tcl list or space seperated values are semantically the same on the
Tcl script level, but as Tkinter fiddles with the intreps for performance
stuff is a bit more fragile as you noticed and there have been some changes
to list handling internally. I would have assumed a python tuple always
gets converted to Tcl list its the natural mapping.

re: bgerror
You should be able to redefine bgerror to do what you want in your startup
and initialization code for tkinter. Just add some Tcl proc named bgerror
there that does what you want.

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Comment By: Martin v. Löwis (loewis)
Date: 2008-01-01 22:06

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This is now fixed in r59653 in the Python repository, for Python 2.6. I
don't think the patch can be backported to 2.5, as it may have other side
effects when Python callbacks stop always returning strings to Tcl.

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Comment By: Martin v. Löwis (loewis)
Date: 2008-01-01 21:16

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I found the source of the problem: Lib.idlelib.WidgetRedirector.dispatch
gets invoked, and invokes the original Tk bbox command. This returns a Tcl
list, which _tkinter converts into a Python tuple, which gets returned from
dispatch. In turn, _tkinter then converts the tuple back, but now returns a
string to Tcl, in the interpreter result, such as "(41, 3, 8, 20)". This
then causes the Tcl error, trying to index that string as a list.

Apparently, in Tcl 8.4, bbox returned a space-separated list of numbers,
instead of a Tcl list. When that got passed through, Tcl would happily
consider it a list again.

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Comment By: Martin v. Löwis (loewis)
Date: 2008-01-01 19:28

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If there was a way for Python to raise a Python exception in _tkerror, so
that Tk's bgerror won't subsequently open a window catching that exception
- that would be a good thing. IIUC, Tkinter._tkerror is empty because there
is no meaningful way to report the error (and Tk's default behavior of
opening a window isn't quite acceptable).

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Comment By: Donal K. Fellows (dkf)
Date: 2007-12-15 23:03

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Very strange: either the X coordinate is non-numeric or the result of
[lindex $bbox 0] is non-numeric. Not sure which is worse.

In general, setting a bgerror handler ought to pick up problems like this.
Problem is, it might conflict with the Tkinter one (which sounds
insufficiently robust against errors from the Tcl side of things...)

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Comment By: George Peter Staplin (georgeps)
Date: 2007-12-15 22:49

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I've discovered that a Tcl callback that Tkinter was evaluating was
throwing an error and therefore not working properly.  However Tkinter
seems to ignore such errors, and there was no report of it to stderr or
otherwise.  :-/

proc ::tk::dump val { puts DUMP:$val; return $val }
proc ::tk::TextButton1 {w x y} {
    variable ::tk::Priv

    set Priv(selectMode) char
    set Priv(mouseMoved) 0
    set Priv(pressX) $x
parray Priv

puts "$w $x $y"
    if {[catch {$w mark set insert [TextClosestGap $w $x $y]} err]} {
         puts ERR:$err
    }
    ...
}

The ERR is: can't use non-numeric string as operand of "-"

Here's where it gets weirder.  For some reason in TextClosestGap the bbox
subcommand is returning garbage like this: BBOX:(43, 3, 6, 10)

This doesn't happen with 8.4.  The same BBOX subcommand in 8.4 returns a
proper *Tcl* list.  All of which leaves me very puzzled.  Perhaps Tkinter
does something differently with 8.4 and assumes older code for the newer
8.5.


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