[Python] Only allow numbers and "."-input in Entries [duplicate]

I only want to input numbers from 0-9 and a "." if I want to input a float number. So far I have this:

def keylistener(event):
ACCEPTED = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "."]
if not event.char in ACCEPTED:
pass
# Dont let the character be inputed
#....

tk.bind('<KeyPress>', keylistener)


can anyone help me?

EDIT: maybe there is another problem in my Program, so I extracted the relevant code and post it here now as the complete Python-file

from tkinter import *

tk = Tk()
tk.title("Only Numbers")
tk.configure(bg="black")
tk_frame = Frame(relief=RAISED,bd=8,bg="gray")
category = StringVar(tk_frame)

def keylistener(event):
ACCEPTED = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "."]
if event.char not in ACCEPTED:
return "break"
# Dont let the character be inputed

entry = Entry(tk_frame,bg="white",fg="black")

tk_frame.grid()
entry.grid(column=1, row=1)

# Start Keylistener
tk.bind('<KeyPress>', keylistener)

tk.mainloop()

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