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Re: Validating Entry in tkinter

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  Re: Validating Entry in tkinter Saul Spatz <saul.spatz@gmail.com> - 2011-07-25 05:12 -0700
    Re: Validating Entry in tkinter Peter Otten <__peter__@web.de> - 2011-07-25 14:31 +0200
      Re: Validating Entry in tkinter Terry Reedy <tjreedy@udel.edu> - 2011-07-25 13:24 -0400
      Re: Validating Entry in tkinter Peter Otten <__peter__@web.de> - 2011-07-25 21:08 +0200
        Re: Validating Entry in tkinter rantingrick <rantingrick@gmail.com> - 2011-07-25 12:55 -0700
      Re: Validating Entry in tkinter python@bdurham.com - 2011-07-25 16:26 -0400
      Re: Validating Entry in tkinter Peter Otten <__peter__@web.de> - 2011-07-25 23:03 +0200
      Re: Validating Entry in tkinter "Malcolm Greene" <mgreene@bdurham.com> - 2011-07-25 17:54 -0400

#10263 — Re: Validating Entry in tkinter

That doesn't work, I'm being stupid,  The user might type anywhere in the string, not just at the end.  I need

return all([c in '1234567890abcdefABCDEF ' for c in after])

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#10265

Saul Spatz wrote:

> That doesn't work, I'm being stupid,  The user might type anywhere in the
> string, not just at the end.  I need
> 
> return all([c in '1234567890abcdefABCDEF ' for c in after])

Ah, you found out already. Here's what I've come up with in the meantime.
I also changed the command to a tuple as in the example pointed out by 
Wolfgang.

import tkinter as tk

def is_valid_fromhex(s):
    for pad in "", "0":
        try:
            bytes.fromhex(s + pad)
        except ValueError:
            pass
        else:
            return True
    return False

def validate(before, after):
    print(before, "-->", after)
    return is_valid_fromhex(after)

if __name__ == "__main__":
    root = tk.Tk()
    cmd = (root.register(validate), "%s", "%P")
    entry = tk.Entry(root, validate="all", validatecommand=cmd)
    entry.pack()
    entry.focus_set()
    root.mainloop()

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#10294

On 7/25/2011 8:31 AM, Peter Otten wrote:
> Saul Spatz wrote:
>
>> That doesn't work, I'm being stupid,  The user might type anywhere in the
>> string, not just at the end.  I need
>>
>> return all([c in '1234567890abcdefABCDEF ' for c in after])

If one wants to validate keystrokes, rather than the entire field after 
the fact, is it possible to set an onkey handler, that will pass on 
valid keys?

-- 
Terry Jan Reedy

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#10298

Terry Reedy wrote:

> On 7/25/2011 8:31 AM, Peter Otten wrote:
>> Saul Spatz wrote:
>>
>>> That doesn't work, I'm being stupid,  The user might type anywhere in
>>> the
>>> string, not just at the end.  I need
>>>
>>> return all([c in '1234567890abcdefABCDEF ' for c in after])
> 
> If one wants to validate keystrokes, rather than the entire field after
> the fact, 

It's not really after the fact as the user will not see the new contents 
unless they are accepted by the validatecommand handler.

> is it possible to set an onkey handler, that will pass on
> valid keys?

With validatecommand you can have tkinter provide the string that is being 
inserted:

import tkinter as tk

MESSAGE = ("about to insert {text!r} at position {index} "
           "({resolution})")

def validate(action, index, text):
    if action == "1":
        accept = text.isdigit()
        print(
            MESSAGE.format(
                resolution="OK" if accept else "rejected",
                text=text,
                index=index))
        return accept
    return True

if __name__ == "__main__":
    root = tk.Tk()
    cmd = (root.register(validate), "%d", "%i", "%S")
    entry = tk.Entry(root, validate="all", validatecommand=cmd)
    entry.pack()
    entry.focus_set()
    root.mainloop()

The available format codes are listed at 
http://www.tcl.tk/man/tcl8.4/TkCmd/entry.htm#M16

If you need something more specific you'd probably have to bind the 
<KeyPress> event to a custom handler:

import tkinter as tk

def keypress(event):
    print(event.char)
    if event.char:
        if not event.char.isdigit() and event.char != "\b":
            return "break"
    else:
        print("Don't know what to do with key #", event.keycode)

if __name__ == "__main__":
    root = tk.Tk()
    entry = tk.Entry(root)
    entry.bind("<KeyPress>", keypress)
    entry.pack()
    entry.focus_set()
    root.mainloop()

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#10306

On Jul 25, 2:08 pm, Peter Otten <__pete...@web.de> wrote:
> Terry Reedy wrote:
> > On 7/25/2011 8:31 AM, Peter Otten wrote:
> >> Saul Spatz wrote:
> > is it possible to set an onkey handler, that will pass on
> > valid keys?
>
> With validatecommand you can have tkinter provide the string that is being
> inserted:

Yes but it's messy and requires knowledge of Tcl! We to keep our code
bases as Pythonic as possible.

> If you need something more specific you'd probably have to bind the
> <KeyPress> event to a custom handler:

Exactly!

If you compare the code of the two approaches you'll see that the
python approach is more readable and does not export any "magic"
behind the scenes. By binding the KeyPress event and handling it in
some derived class people who are not familiar with Tcl\Tk can read
the code (and change it to suit their needs). The next best
alternative would be to extend Tk.Entry with a pythonic wrapper for
this functionality.

MORAL: Sometimes you are forced to export these things but in this
case i would argue that readability counts; so keep it in Python!

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#10307

Peter,

How would your examples work with text being inserted or deleted via the
clipboard?

Is there anything special that would have to happen for changes to a
widget's value as the result of one of these events?

Thank you,
Malcolm (not the OP)

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#10310

python@bdurham.com wrote:

> How would your examples work with text being inserted or deleted via the
> clipboard?
> 
> Is there anything special that would have to happen for changes to a
> widget's value as the result of one of these events?

I think it doesn't matter whether you type in text, or insert it with Ctrl+V 
or the middle mouse button. The validatecommand handler is always triggered.

I suspect achieving the same effect with Button/KeyPress handlers would 
require significantly more work.

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#10315

Peter,

> I think it doesn't matter whether you type in text, or insert it with Ctrl+V or the middle mouse button. The validatecommand handler is always triggered. I suspect achieving the same effect with Button/KeyPress handlers would require significantly more work.

Thank you!
Malcolm

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