from tkinter import simpledialog
from tkinter import *
def s():
 print(simpledialog.askstring("hai","inp"))

root = Tk()
b = Button(root, text="popup",command=s)
b.pack()

root.geometry("400x400")
root.mainloop()

Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1550, in __call__
    return self.func(*args)
  File "popup.py", line 4, in s
    print(simpledialog.askstring("hai","inp"))
AttributeError: 'module' object has no attribute 'askstring'