from tkinter import *
from tkinter import ttk
from tkinter import messagebox

root=Tk()
varx=DoubleVar()
def com(event):
    #messagebox.showinfo('error', 'bum')
    l.config(text='error')
spin=ttk.Spinbox(root, from_=-50, to=50, textvariable=varx)
spin.bind('<Button-1>', com)
spin.pack()
l = Label(root, text = '')
l.pack()
root.mainloop()