Using bound variables in Tkinter events

**wes weston** · Jul 18 '05, 09:55 AM

Re: Using bound variables in Tkinter events

Derek Fountain wrote:[color=blue]
> I'm coming to Tkinter from Tcl/Tk. In Tcl I can get a variable in an event
> using the %<X> substitution mechanism. For example, I can set up a command
> like:
>
> entry .e -validate 1 -vcmd "checkkey %d"
>
> knowing that the '%d' will be replaced by something useful - whether the
> entry widget has recieved an insert or deletion in this case. The checkkey
> procedure will recieve "insert", "delete" or whatever as its first
> parameter.
>
> What is the Tkinter way of getting that %d value?[/color]

Derek,
f = Entry()
....
v = StringVar()
v.set("test")
f["textvariab le"] = v

print v.get()

**Peter Otten** · Jul 18 '05, 09:56 AM

Re: Using bound variables in Tkinter events

Derek Fountain wrote:
[color=blue]
> I'm coming to Tkinter from Tcl/Tk. In Tcl I can get a variable in an event
> using the %<X> substitution mechanism. For example, I can set up a command
> like:
>
> entry .e -validate 1 -vcmd "checkkey %d"
>
> knowing that the '%d' will be replaced by something useful - whether the
> entry widget has recieved an insert or deletion in this case. The checkkey
> procedure will recieve "insert", "delete" or whatever as its first
> parameter.
>
> What is the Tkinter way of getting that %d value?[/color]

import Tkinter as tk
root = tk.Tk()

def check(action):
print {"1":"inserting ", "0": "deleting"}.get (action, "should never
happen")
return True
checkId = root.register(c heck)

entry = tk.Entry(root, validate="key", validatecommand =checkId + " %d")
entry.pack()
root.mainloop()

The above was found by trial and error, so no warranties :-)
You could use check() directly, like

entry = tk.Entry(root, validate="key", validatecommand =check)

but then it will be called without parameters.

Peter

**John Roth** · Jul 18 '05, 09:56 AM

Re: Using bound variables in Tkinter events

"Derek Fountain" <devnull@exampl e.com> wrote in message
news:4067a227$0 $16577$5a62ac22 @freenews.iinet .net.au...[color=blue]
> I'm coming to Tkinter from Tcl/Tk. In Tcl I can get a variable in an event
> using the %<X> substitution mechanism. For example, I can set up a command
> like:
>
> entry .e -validate 1 -vcmd "checkkey %d"
>
> knowing that the '%d' will be replaced by something useful - whether the
> entry widget has recieved an insert or deletion in this case. The checkkey
> procedure will recieve "insert", "delete" or whatever as its first
> parameter.
>
> What is the Tkinter way of getting that %d value?[/color]

It's in the event object that's passed as the (only) parameter
to your event handler. Everything you ever wanted to know
about the event is an attribute.

There are a number of very good references to Tkinter on
the first page of the Python Library Reference section on
Tkinter. (That's section 16 in the Python 2.3 reference)

John Roth

**Derek Fountain** · Jul 18 '05, 09:57 AM

Re: Using bound variables in Tkinter events

wes weston wrote:
[color=blue]
> Derek Fountain wrote:[color=green]
>> I'm coming to Tkinter from Tcl/Tk. In Tcl I can get a variable in an
>> event using the %<X> substitution mechanism. For example, I can set up a
>> command like:
>>
>> entry .e -validate 1 -vcmd "checkkey %d"
>>
>> knowing that the '%d' will be replaced by something useful - whether the
>> entry widget has recieved an insert or deletion in this case. The
>> checkkey procedure will recieve "insert", "delete" or whatever as its
>> first parameter.
>>
>> What is the Tkinter way of getting that %d value?[/color]
>
> Derek,
> f = Entry()
> ...
> v = StringVar()
> v.set("test")
> f["textvariab le"] = v
>
> print v.get()[/color]

Thanks, but that's not what I was after! I want to know the type of action
I've received - the %d binding for the validatecommand .

**Derek Fountain** · Jul 18 '05, 09:57 AM

Re: Using bound variables in Tkinter events

>> I'm coming to Tkinter from Tcl/Tk. In Tcl I can get a variable in an[color=blue][color=green]
>> event using the %<X> substitution mechanism. For example, I can set up a
>> command like:
>>
>> entry .e -validate 1 -vcmd "checkkey %d"
>>
>> knowing that the '%d' will be replaced by something useful - whether the
>> entry widget has recieved an insert or deletion in this case. The
>> checkkey procedure will recieve "insert", "delete" or whatever as its
>> first parameter.
>>
>> What is the Tkinter way of getting that %d value?[/color]
>
> It's in the event object that's passed as the (only) parameter
> to your event handler. Everything you ever wanted to know
> about the event is an attribute.[/color]

The validate command doesn't get an event.
[color=blue]
> There are a number of very good references to Tkinter on
> the first page of the Python Library Reference section on
> Tkinter. (That's section 16 in the Python 2.3 reference)[/color]

Indeed, but I couldn't find anything which answered this question.

**Derek Fountain** · Jul 18 '05, 09:57 AM

Re: Using bound variables in Tkinter events

> import Tkinter as tk[color=blue]
> root = tk.Tk()
>
> def check(action):
> print {"1":"inserting ", "0": "deleting"}.get (action, "should never
> happen")
> return True
> checkId = root.register(c heck)
>
> entry = tk.Entry(root, validate="key", validatecommand =checkId + " %d")
> entry.pack()
> root.mainloop()
>
> The above was found by trial and error, so no warranties :-)[/color]

Awesome, thank you. I don't understand what's going on though. Can you
explain a bit? I don't understand the mechanism which is expanding the %d.
Is there some magic in the tk.Entry constructor which does it, or is that
root.register() doing something clever?

[color=blue]
> You could use check() directly, like
>
> entry = tk.Entry(root, validate="key", validatecommand =check)
>
> but then it will be called without parameters.[/color]

That's as far as I'd got and I was beginning to think it was impossible to
get the parameters. At least I now know it can be done, even if I don't
understand how!

**Peter Otten** · Jul 18 '05, 09:57 AM

Re: Using bound variables in Tkinter events

Derek Fountain wrote:
[color=blue][color=green]
>> import Tkinter as tk
>> root = tk.Tk()
>>
>> def check(action):
>> print {"1":"inserting ", "0": "deleting"}.get (action, "should never
>> happen")
>> return True
>> checkId = root.register(c heck)
>>
>> entry = tk.Entry(root, validate="key", validatecommand =checkId + " %d")
>> entry.pack()
>> root.mainloop()
>>
>> The above was found by trial and error, so no warranties :-)[/color]
>
> Awesome, thank you. I don't understand what's going on though. Can you
> explain a bit? I don't understand the mechanism which is expanding the %d.
> Is there some magic in the tk.Entry constructor which does it, or is that
> root.register() doing something clever?[/color]

register() wraps a python function into a tcl function and returns the new
tcl function's name (can they start with a number?). If you provide a
string instead of a python function reference as a callback for (e. g.)
validatecommand , it is passed unaltered to tcl.
That's all there is to it - at least so my theory goes.

Peter

**Cameron Laird** · Jul 18 '05, 10:01 AM

Re: Using bound variables in Tkinter events

In article <c4gf64$3df$04$ 1@news.t-online.com>,
Peter Otten <__peter__@web. de> wrote:

Using bound variables in Tkinter events

Using bound variables in Tkinter events

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