Create dynamically updatable progress bar

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Hi!

Sometimes calculations takes a long time, and it'll be very useful to know the progress. A simple example:

from time import sleep

def slow_calculations():
    for i in range(10):
        sleep(0.5)
        print 'Complete',(i+1)*10,'%'
    print 'Done'

Such indication of process was my first solution. Is is possible somehow to draw a progress bar and update it's value during the calculations? Something like that:

def slow_calculations(bar):
    for i in range(10):
        sleep(0.5)
        bar.value = (i+1)*10

progressBar= ProgressBar()
progressBar.show()
slow_calculations(progressBar)