Creating a popup message box with an Entry field

I want to create a popup message box which prompts user to enter an input. I have this method inside a class. I am basing my code on this guide by java2s.

class MyDialog:
    def __init__(self, parent):
        top = self.top = Toplevel(parent)

        Label(top, text="Value").pack()

        self.e = Entry(top)
        self.e.pack(padx=5)

        b = Button(top, text="OK", command=self.ok)
        b.pack(pady=5)

    def ok(self):
        print "value is", self.e.get()
        self.top.destroy()

root = Tk()
d = MyDialog(root)

root.wait_window(d.top)

But in this, top = self.top = Toplevel(parent) doesn't work for me.

I have a mockup of what I am trying to accomplish.

My program structure looks something like this:

class MainUI:
   def__int__(self):
       ...
       self.initUI()

   def initUI(self):
       .......
       Popup = Button(self, text="Enter Value", command=self.showPopup)

   def showPopup(self):
       #create the popup with an Entry here

How can I create a message box in Python which accepts user input?

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: