Creating a popup message box with an Entry field

I did it in Tkinter without any classes. I created a function that starts a new window.

popup.Tk()
popup.mainloop()

In that window there is an Entry field from where I get the text with a variable which value is: entry.get()

Then you can use that variable for whatever you need and it will take the text from that Entry field.

import tkinter as tk
from tkinter import simpledialog

ROOT = tk.Tk()

ROOT.withdraw()
# the input dialog
USER_INP = simpledialog.askstring(title="Test",
                                  prompt="What's your Name?:")

# check it out
print("Hello", USER_INP)

Enjoy ...

I'm a little confused about your two different blocks of code. Just addressing the first block of code, nothing happens because you never enter the mainloop. To do that, you need to call root.mainloop(). The typical way of doing this is to add a button to root widget and bind a callback function to the Button (which includes d=MyDialog() and root.wait_window(d.top))

Here's some basic code which I hope does what you want ...

from Tkinter import *
import sys

class popupWindow(object):
    def __init__(self,master):
        top=self.top=Toplevel(master)
        self.l=Label(top,text="Hello World")
        self.l.pack()
        self.e=Entry(top)
        self.e.pack()
        self.b=Button(top,text='Ok',command=self.cleanup)
        self.b.pack()
    def cleanup(self):
        self.value=self.e.get()
        self.top.destroy()

class mainWindow(object):
    def __init__(self,master):
        self.master=master
        self.b=Button(master,text="click me!",command=self.popup)
        self.b.pack()
        self.b2=Button(master,text="print value",command=lambda: sys.stdout.write(self.entryValue()+'\n'))
        self.b2.pack()

    def popup(self):
        self.w=popupWindow(self.master)
        self.b["state"] = "disabled" 
        self.master.wait_window(self.w.top)
        self.b["state"] = "normal"

    def entryValue(self):
        return self.w.value


if __name__ == "__main__":
    root=Tk()
    m=mainWindow(root)
    root.mainloop()

I get the value from the popupWindow and use it in the main program (take a look at the lambda function associated with b2).

Main window:

"Click me" window:

Main window while "click me" is open: