Some oddities in 2.3b1, esp. with Tkinter

[Russell E. Owen]

I finally got my app almost running in 2.3b1. I've run into the 
following:

1) A filter to remove fonts with non-ascii names (used to filter out 
stuff that I could not display in a pop-up menu) broke.
            try:
                unicode(fontName, 'ascii', 'strict')
                return True
            except UnicodeError:
                return False

Python 2.2 throws UnicodeError. Python 2.3b1 throws TypeError. The fix 
is trivial (e.g. "except (UnicodeError, TypeError)". The filter is 
probably not needed anymore anyway, since Tk 8.4.2 can apparently 
display menu items with non-ascii characters.

2) Tk file events are no longer supported:

RuntimeError: _tkinter.createfilehandler not supported for threaded Tcl

This is painful since it's hard to see how to write a proper networking 
GUI with Tkinter without file events for reading data. Perhaps I can get 
them back again by disabling the new threaded tcl support. However, I 
suspect it's time to try out the Twisted framework.

3) Tk returning things as objects is nice, but I had this break at least 
one thing of mine and it will break others (see 4 below):

I was assuming that the values in the dictionary returned by 
tkFont.Font.config() were strings. Fortunately this was easy to fix. A 
bit disconcerting -- I wonder how many any other little pitfalls like 
this still buried in my code -- but well worth the cost of the change.

4) Tk Variables are trickier to use and the change will break some 
existing code.

Tkinter used to return a variable name if the variable of a widget was 
requested. Not as convient as returning the original variable, but once 
one found the magic setvar and getvar functions (which work on variable 
names) things were fine.

Now Tk returns a _tkinter.Tcl_Obj instead, and and setvar and getvar 
don't seem to work on that. (I'm relieved that I never actually used 
setvar and getvar in my final code; despite many temptations I was 
always uncomfortable with it).

Example:
v = StringVar()
v is a <Tkinter.StringVar instance at 0x2c98a0>
l = Label(textvariable=v)
x = l["textvariable"]
x is reported as a <namespaceVarName object at 0x0168b048>
but is a _tkinter.Tcl_Obj based on the following traceback:
root.getvar(x)
Traceback...
TypeError: getvar() argument 1 must be string, not _tkinter.Tcl_Obj

Note that x.get() doesn't work either -- i.e. the object does not mimic 
a Tk Variable. I'm guessing there is some way to manage this, but have 
no idea what it might be.

5) Note that Tkinter's handling of font objects does not seem to have 
changed. I was hoping it would start returning font objects instead of 
strings, or offer some way to convert the string to a font object, but 
apparently not:
f = tkFont.Font(font="system")
l = Label(font=f)
l["font"] returns: 'font2922816'

-- Russell