I've written essentially this many times in the last 18 months.

reticulator.py

class Reticulator(object):
    def __init__(self, n):
        self.n = n
        self.i = 0

    def tick(self):
        self.i += 1
        if (self.i - 1) % 100 == 0 or self.i + 1 >= self.n:
            sys.stderr.write('[{}/{}]\r'.format(self.i, self.n))

One incarnation I wrote at GSA had a spinner, estimated time remaining, etc. Wish I'd written it in my spare time so I could have kept it.