Python - tkinter - second window with StringVar

import tkinter as tk


class Main(tk.Tk):

    def __init__(self):
        super().__init__()

        self.l = tk.Label(self, text='???')
        self.l.pack()

        b = tk.Button(self, text='New', command=self.on_click)
        b.pack()

        self.mainloop()

    def on_click(self):
        new = Next(self)
        print('close')


class Next(tk.Toplevel):

    def __init__(self, master): # master - to get access to parent window
        super().__init__(master)

        self.var = tk.StringVar() # tk.StringVar(self)

        e = tk.Entry(self, textvariable=self.var)
        e.pack()

        b = tk.Button(self, text='Close', command=self.on_click)
        b.pack()

        #self.mainloop() # no need it

    def on_click(self):
        print(self.var.get()) # get text from Entry
        self.master.l['text'] = self.var.get() # put in parent window
        self.destroy()


Main()