gistfile1.py

class ProgressBar(object):
    def __init__(self, n, current=0, width=40, output=sys.stdout):
        self.n = n
        self.current = current
        self.width = width
        self.step = self.n / self.width
        self.output = output

    def draw_one(self):
        self.output.write("-")

    def draw(self):
        for _ in xrange(self.current):
            self.poke()

    def poke(self, n=1):
        if self.current > self.n:
            raise ValueError("ProgressBar overflowed.")
        diff = int((self.current + n) / self.step) - int(self.current / self.step)
        for _ in xrange(diff):
            self.draw_one()
        self.current += n