How to handle errors in input in an entry in tkinter with the azure theme ttk

Today we are going to see how to manage errors in tkinter, meaning: how can we get a feedback when the user input is not right. We are going to make a first simple example in which and entry becomes red (the border will become red) when the input is not what we expected.

This is when it’s right

This is not valid

The code

import tkinter as tk
import tkinter.ttk as ttk
from PIL import ImageTk
# create the window
root= tk.Tk()
root.title("Example Error handling")
root.geometry("400x200")

# Give it this theme (put the folder azure dark here
style = ttk.Style(root)
root.tk.call('source', 'theme/azure dark/azure dark.tcl')
style.theme_use('azure')

# Entry widget
strvar= tk.IntVar()
entry = ttk.Entry(root,textvariable=strvar)
entry.place(x=10,y=10)
def check():
    print(entry.get())
    button.config(relief="flat")
    if int(entry.get()) < 1:
        entry.state(["invalid"])
    else:
        entry.state(["!invalid"])

btnimage = ImageTk.PhotoImage(file=('button.png'))
button=tk.Button(root,
    image=btnimage,
    bd=0,
    activebackground="#333333",
    relief="flat",
    text="Click",
    compound=tk.CENTER,
    command=check)
button.place(x=5,y=50)
root.mainloop()

The repository with all the files (images and the theme): here it is.