Validate command not working in Tkinter

Question

In this program, I am attempting to check if an input matches a certain word (in this case 'APPLE') however the vcmd doesn't seem to be recognised - any ideas?

from tkinter import *

class Window(Frame):
    def __init__(self, parent):
        Frame.__init__(self, parent)

        self.vmcd1 = parent.register(self.validate_entry)

        self.title = Label(self, text='Enter here:')
        self.title.pack()

        self.entry = Entry(self, validatecommand=(self.vcmd1,'%P'))
        self.entry.pack()


        self.entered=Label(self, text='You entered')
        self.entered.pack()

    def callback(self):
        self.entered.config(text='You entered: ' + self.entry.get())

    def validate_entry(self, entry):
        print('Code validates entry')
        if entry == 'APPLE':
            print('This input is correct.')
        else:
            pass


root = Tk()
frame = Window(root)
frame.pack()
root.mainloop()

You define `self.vmcd1`, then use `self.vcmd1` as validatecommand. That's a typo. — fhdrsdg, Jun 19 '18 at 10:57
Also, the validatecommand function should only return `True` or `False` to allow or disallow the edit. And you should define when to validate the entry with the `validate` argument, you can find the options [here](http://effbot.org/tkinterbook/entry.htm#Tkinter.Entry.config-method) under `validate=`. — fhdrsdg, Jun 19 '18 at 11:03
There's a nice example of validation [here](https://stackoverflow.com/a/4140988/4014959). Apart from the problems previously mentioned, your `validate_entry` is problematic: unless the user pastes 'APPLE' into the widget nothing will pass validation. — PM 2Ring, Jun 19 '18 at 11:27

score 3 · Accepted Answer · answered Jun 19 '18 at 20:03

To summarize what is said in the comments:

There is a typo in the validate command name: you wrote self.vmcd1 = ... instead of self.vcmd1 = ...
Your validate command should return True (accept change) or False (reject change). If I understand correctly what you want to achieve, your function should always return True, but do something special if the content of the entry is 'APPLE'.
```
def validate_entry(self, entry):
    print('Code validates entry')
    if entry == 'APPLE':
        print('This input is correct.')
    return True
```
Your validate command is never executed because the default value for the validate option is 'none'. You need to set this option to 'key' for instance if you want the content of the entry to be checked each time the user types something (more possible values here)
```
    self.entry = Entry(self, validatecommand=(self.vcmd1, '%P'), validate='key')
```

Validate command not working in Tkinter

1 Answers1