autoscroll of text and scrollbar in python text box

Take a look at Text.see(...) method.

TextWidget.insert(tk.END, str(new_txt))
TextWidget.see(tk.END)

I used this pattern to add (aka insert) text new_txt to my output window and scroll (see) to the bottom (tk.END)

You can cause the text widget to scroll to any location with the see which takes an index.

For example, to make the last line of the widget visible you can use the index "end":

outputwindow.see("end")

Here's a complete working example:

import time
try:
    # python 2.x
    import Tkinter as tk
except ImportError:
    # python 3.x
    import tkinter as tk

class Example(tk.Frame):
    def __init__(self, *args, **kwargs):
        tk.Frame.__init__(self, *args, **kwargs)

        self.text = tk.Text(self, height=6, width=40)
        self.vsb = tk.Scrollbar(self, orient="vertical", command=self.text.yview)
        self.text.configure(yscrollcommand=self.vsb.set)
        self.vsb.pack(side="right", fill="y")
        self.text.pack(side="left", fill="both", expand=True)

        self.add_timestamp()

    def add_timestamp(self):
        self.text.insert("end", time.ctime() + "\n")
        self.text.see("end")
        self.after(1000, self.add_timestamp)

if __name__ == "__main__":
    root =tk.Tk()
    frame = Example(root)
    frame.pack(fill="both", expand=True)
    root.mainloop()