data entry validation with Tkinter

[Joseph A. Knapka]

Ken Guest wrote:
> 
> hi,
> I'm trying to put together a python + tkinter app with data entry
> validation.
> What I have in mind is that the colour of the text changes depending
> on what the user has typed. (In otherwords the text is displayed in
> red if it is invalid, and in black if it is ok).
> I'd like to use regex (or the more up-to-date re strings) to specify
> what type of text is valid (cf my last query to the help mailing list).
> 
> At the moment, basic code that I have gotten to work looks like:
> 
> self.__entry = Entry(newframe, validate='key', vcmd='string is int %P',
> invcmd='bell')
> 
> attempts at specifying python procedures for vcmd and invcmd only seem
> to be called when the app in initialising and don't exactly work.
> For example, with
> 
> self.__entry = Entry(newframe, validate='key', vcmd=self.validate('%P'),
>                      invcmd=self.invalid())

This is because self.validate('%P') is a method call, not a
bound method object. Similarly self.invalid() - you're calling
the method and sending its result into the Entry() call.

I have a similar problem - I need to send data known at
control-creation time to the callback when the control is
clicked. So I use a callable object and attach the data to
it:

class CallbackCmd:

	def __init__(self,boundmethod,data):
		self.boundmethod = boundmethod
		self.data = data

	def __call__(self,*args):
		apply(boundmethod,(self.data,)+*args)

Then:

class SomeGUI:

	def theCallback(self,data,*args):
		doSomethingUseful(data)

	def __init__(self,someCallbackData):
		btn = Tkinter.Button(command=CallbackCmd(
					self.theCallback,
					someCallbackData)
					)

and then when the btn is clicked, SomeGUI.theCallback() is
invoked with someCallbackData as the first argument, and
the rest of the Tk callback arguments following.

I wonder if there is a more Pythonian way to accomplish this?

HTH,

-- Joe

> the validate and invalid methods are called when the app starts up, but
> neither of those methods are called when any keys are pressed, and I'm
> really not sure that the second definition above is syntatically
> correct, even though the parser didn't catch any problems.
> 
> What I'd like to know is if what I am looking to do is in anyway
> possible, and if anybody has any pointers/ideas on how I could
> implement this functionality.
> Am I left to using TCL expressions for data entry validation (and if so,
> how do I do the above)
> 
> (I have done a number of searches on Google to see if anybody else
> may have run into these questions before but couldn't find anything
> of interest)
> 
> thanks,
> 
> Ken

-- Joe Knapka
"You know how many remote castles there are along the gorges? You
 can't MOVE for remote castles!" -- Lu Tze re. Uberwald
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