Python Tkinter 入口 get()

Question

I'm trying to use Tkinter's Entry widget. I can't get it to do something very basic: return the entered value.
Does anyone have any idea why such a simple script would not return anything? I've tried tons of combinations and looked at different ideas.
This script runs but does not print the entry:

from Tkinter import *
root = Tk()
E1 = Entry(root)
E1.pack()
entry = E1.get()
root.mainloop()
print "Entered text:", entry

Seems so simple.

Edit: In case anyone else comes across this problem and doesn't understand, here is what ended up working for me. I added a button to the entry window. The button's command closes the window and does the get() function:

from Tkinter import *
def close_window():
    global entry
    entry = E.get()
    root.destroy()

root = Tk()
E = tk.Entry(root)
E.pack(anchor = CENTER)
B = Button(root, text = "OK", command = close_window)
B.pack(anchor = S)
root.mainloop()

And that returned the desired value.

Answer 1

Your first problem is that the call to get in entry = E1.get() happens even before your program starts, so clearly entry will point to some empty string.

Your eventual second problem is that the text would anyhow be printed only after the mainloop finishes, ie you close the tkinter application.

If you want to print the contents of your Entry widget while your program is running, you need to schedule a callback. For example, you can listen to the pressing of the <Return> key as follows

import Tkinter as tk


def on_change(e):
    print e.widget.get()

root = tk.Tk()

e = tk.Entry(root)
e.pack()    
# Calling on_change when you press the return key
e.bind("<Return>", on_change)  

root.mainloop()

Answer 2

from tkinter import *
import tkinter as tk
root =tk.Tk()
mystring =tk.StringVar(root)
def getvalue():
    print(mystring.get())
e1 = Entry(root,textvariable = mystring,width=100,fg="blue",bd=3,selectbackground='violet').pack()
button1 = tk.Button(root, 
                text='Submit', 
                fg='White', 
                bg= 'dark green',height = 1, width = 10,command=getvalue).pack()

root.mainloop()