file_size = os.path.getsize('some/file.txt')
with open('some/file.txt') as stream:
    for line in stream:
        # some parsing algorithm

class Progressor:
    def __init__(self, overall):
        self.overall = overall
        self.utilized = 0
    def progress(self, amount)
        self.utilized += amount
        return float(self.utilized) / self.overall