How to make simpledialog askstring in Python Tkinter?

 

from tkinter import *
from tkinter.simpledialog import askstring


class learn():
    def __init__(self, root):
        self.root=root
        self.root.title("Hancie e-Learning Studio")
        self.root.geometry("500x400")

        def dialog():
            prompt = askstring("Input", "Input an String")
            print(prompt)

        btn=Button(self.root,command=dialog, text="Open dialog")
        btn.pack()



if __name__=='__main__':
    root=Tk()
    learn(root)
    root.mainloop()

Output