I want an Entry widget to accept a single digit only. Here's the attempt:
---
import Tkinter as Tk
class MyEntry(Tk.Entry):
def __init__(self, parent, **kwargs):
kwargs['validate']='key' # could also be 'all' -- has the
same result
kwargs['vcmd']=self.validate
Tk.Entry.__init__(self, parent, **kwargs)
def validate(self):
print self.get() # diagnostic only
if self.get() in [''] + list("123456789"):
return True
else:
self.bell()
return False
if __name__=="__main__":
main = Tk.Tk()
main.e = MyEntry(main)
main.e.grid()
main.mainloop()
---
I'd like to think this is straightforward, but No.
I type in MyEntry: 1
printed value: (empty string)
contents of MyEntry: 1
I type in MyEntry: 11
printed value: 1
contents of MyEntry: 11
I type in MyEntry: 111 (bell rings)
printed value: 11
contents of MyEntry: 11
I type in MyEntry: a
printed value: (empty string)
contents of MyEntry: a
I type in MyEntry: a1 (bell rings)
printed value: a
contents of MyEntry: a
Near as I can tell, validate() is called after a key is pressed and
displayed in the Entry widget, but *before* the pressed key has been
added to MyEntry's contents. Hence, validate() has no way of knowing
what the new keypress is -- it can only validate the past entry. Once
it does so, the new key is added to MyEntry's contents.
How can validate() discover the new keypress in order to validate it
prior to addition to the Entry widget? Yikes!
Thanks in advance,
Jeff Cagle
_______________________________________________
Tkinter-discuss mailing list
Tkinter-discuss@python.org
http://mail.python.org/mailman/listinfo/tkinter-discuss
