A simple progress bar, showing a spinner, and featuring deferred polling which can easily be replaced. To use this as-is, create a file called 'progress' next to the script, and `echo 0 > progress`. Then, echo your new progress into it, and watch the bar update.

progress_bar.py

#!/usr/bin/env python

from os import popen
from sys import stdout
from time import sleep

largest_max = 0
while True:
    with open('progress') as f:
        progress = int(f.read()) or 0

    # Set the time to wait before polling the progress in the xrange, in seconds:
    for i in xrange(10):
        w = int(popen('stty size', 'r').read().split()[1])
        largest_max = max(largest_max, w)
        for char in ['/', '-', '\\', '|']:
            line = '['
            bar_length = int((w - 8) * (progress / 100.0))
            line += '=' * bar_length
            if progress == 100:
                line += '='
            else:
                line += char
            line = line.ljust(w - 6)
            line += '] ' + str(progress).rjust(3) + '%'

            stdout.write(' ' * largest_max)         # Clear the line forwards
            stdout.write('\b' * (largest_max * 2))  # Clear the line backwards
            stdout.write(line)                      # Write the line
            stdout.flush()                          # Flush the line
            sleep(0.25)                             # Sleep 1/4 of a second, for 4 chars

    if progress == 100:
        break