Input Validation

Sometimes you want to restrict what a use can input into a field. Maybe you have a zipcode field and want to make sure only numbers are entered and it's no longer than 5 digits.

Perhaps you need a floating point number and only want to allow 0-9, ., and -. One way restrict the user's input to only those characters is to get an event any time the user inputs a character and if the character isn't a valid one, remove it.

You've already seen (above) that to get an event immediate when an element is interacted with in some way you set the enable_events parameter.

import PySimpleGUI as sg

"""
    Restrict the characters allowed in an input element to digits and . or -
    Accomplished by removing last character input if not a valid character
"""

layout = [  [sg.Text('Input only floating point numbers')],
            [sg.Input(key='-IN-', enable_events=True)],
            [sg.Button('Exit')]  ]

window = sg.Window('Floating point input validation', layout)

while True:
    event, values = window.read()
    if event in (sg.WIN_CLOSED, 'Exit'):
        break
    # if last character in input element is invalid, remove it
    if event == '-IN-' and values['-IN-'] and values['-IN-'][-1] not in ('0123456789.-'):
        window['-IN-'].update(values['-IN-'][:-1])
window.close()

This code only allows entry of the correct characters.

Note that this example does not fully validate that the entry is a valid floating point number, but rather that it has the correct characters.

If you wanted to take it a step further and verify that the entry is actually a valid floating point number, then you can change the "if" statement to test for valid floating point number.

import PySimpleGUI as sg

"""
    Restrict the characters allowed in an input element to digits and . or -
    Accomplished by removing last character input if not a valid character
"""

layout = [  [sg.Text('Input only floating point numbers')],
            [sg.Input(key='-IN-', enable_events=True)],
            [sg.Button('Exit')]  ]

window = sg.Window('Floating point input validation', layout)

while True:
    event, values = window.read()
    if event in (sg.WIN_CLOSED, 'Exit'):
        break
    # if last character in input element is invalid, remove it
    if event == '-IN-' and values['-IN-']:
        try:
            in_as_float = float(values['-IN-'])
        except:
            if len(values['-IN-']) == 1 and values['-IN-'][0] == '-':
                continue
            window['-IN-'].update(values['-IN-'][:-1])
window.close()