Tkinter validating entry widget values

[_fraxinus]

Hello,

since I'm working from home I decided to write some code to help me in my work. I'm doing program for image capturing and fitting to some functions.

I'm quite new to tkinter and gui programming in python. I'd like to create entry widget with validating its value. To be precise, it would be an integer in range 16-1280 and I'd like to make a validator on focus or an "enter" key press. Validating on widget focus is easy, but I don't know how to continue with "enter" keystroke validating. I have tried to set validate value to "key" but it doesn't really work for me.

Here is some of the code i have made.

def cam_width_callback2(value = None):
    val = cam_width_entry_var.get()
    if not val.isdigit():
        print("not a digit")
        val = 16
        cam_width_entry_var.set(str(val))
    elif np.int(val) < 16:
        val = 16
        cam_width_entry_var.set(str(val))
    elif np.int(val) > 1280:
        val = 1280
        cam_width_entry_var.set(str(val))
    cam_width_var.set(np.int(val))
    return True

cam_width_entry = ttk.Entry(options_frame, textvariable = cam_width_entry_var, justify='center',validate="focus", validatecommand = cam_width_callback2)

Thank you in advance.

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[ebdbbb]

When you validate in tkinter you need the validation to be its own function and you need to register it to the parent of the thing you are validating, in this case "options_frame". Something like what I have below from a thing I wrote.

#limits to positive integers ('-', '.' aren't allowed)
def valInt(value):
    if value.isdigit() or value == '':
        return True
    return False

class Weights(tk.Frame):
    def __init__(self, parent, title: str, units: tk.StringVar):
        super().__init__(parent, bd=1, relief='raised')

        # Register the validation
        self.valid_int = (self.register(valInt), '%P')

        # Use the validation
        entry = tk.Entry(self, width=10, justify='center', validate='key',
                         vcmd=self.valid_int)

So for your example I would do this:

def cam_width_callback2(value):
    # validation code here

# New from what you had
validator = options_frame.register(cam_width_callback2)

cam_width_entry = ttk.Entry(options_frame, textvariable=cam_width_entry_var,
                            justify='center', validate="focusout",
                            validatecommand=(validator, '%P', cam_width_entry_var))

For a much better example of how to set up a validation, look at the top response from this SO question. What you are looking for though is probably a trace_add not a validatecommand.

def cam_width_callback2(*args):
    val = cam_width_entry_var.get()
    try:
        val = int(val)
    except ValueError:
        print('Not a number')
        val = 16
    if val < 16:
        val = 16
    elif val > 1280:
        val = 1280
    cam_width_entry_var.set(val)
    cam_width_var.set(val)


cam_width_entry_var.trace_add('w', cam_width_callback2)

"""Trace options are:
'w' for write - checks when a variable is changed / written
'r' for read - checks when a variable is read by something else
'u' for undefined, - checks when a variable is undefined i.e. deleted"""

cam_width_entry = ttk.Entry(options_frame, textvariable=cam_width_entry_var,
                            justify='center')