如何从tkinter entry小部件获取值，以便可以验证它？

import tkinter as tk

def validate_entry():
    value = entry.get()
    if value.isdigit():
        print("Valid input")
    else:
        print("Invalid input")

root = tk.Tk()

entry = tk.Entry(root)
entry.pack()

button = tk.Button(root, text="Validate", command=validate_entry)
button.pack()

root.mainloop()