Validating Tkinter Entry Box

Question

I am trying to validate my entry box, that only accepts floats, digits, and operators (+×÷-, % ). But my program only accepts numbers not symbols.

I think it is a problem with my conditions or Python Regex.

Here's the code:

from tkinter import *
import re

root = Tk()
def correct(inp):
    pattern = re.compile(r'^(\d*\.?\d*)$')
    if pattern.match(inp) is not None:
        return True
    elif inp is "":
        return True
    else:
        return False

a = Entry(root)
e = root.register(correct)
a.config(validate='key', validatecommand=(e, '%P'))
a.pack()

root.mainloop()

Answer 1

Your regexp only matches floats: \\d*.?\\d* matches digits followed optionally by a dot and more digits. If what you want to match is a pattern like [float][operator][float], then you can use (just add the operators you want in the square brackets):

pattern = re.compile(r'^\d*\.?\d*[+*/\-%]?\d*\.?\d*$')

If you don't care about the order and just want to allow any sequence of numbers and operators:

pattern = re.compile(r'^[\d.+*/\-%]*$')