Using bound variables in Tkinter events

Derek Fountain

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?

Jul 18 '05 #1

wes weston

Derek Fountain wrote:

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?

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

print v.get()

Jul 18 '05 #2

Peter Otten

Derek Fountain wrote:

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?

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(check)

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

Jul 18 '05 #3

John Roth

"Derek Fountain" <de*****@example.com> wrote in message
news:40***********************@freenews.iinet.net. au...

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?

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

Jul 18 '05 #4

Derek Fountain

wes weston wrote:

Derek Fountain wrote:

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?

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

print v.get()

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.

Jul 18 '05 #5

Derek Fountain

>> 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?
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.

The validate command doesn't get an event.
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)

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

Jul 18 '05 #6

Derek Fountain

> 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(check)

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

The above was found by trial and error, so no warranties :-)
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?

You could use check() directly, like

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

but then it will be called without parameters.

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!

Jul 18 '05 #7

Peter Otten

Derek Fountain wrote:

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(check)

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

The above was found by trial and error, so no warranties :-)

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?

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

Jul 18 '05 #8

Cameron Laird

In article <c4*************@news.t-online.com>,
Peter Otten <__*******@web.de> wrote:

Jul 18 '05 #9