"""Example of a generator: re-implement the built-in range functionwithout actually constructing the list of values. OldStyleRange is coded in the way required to work in a 'for' loop beforeiterators were introduced into the language; using __getitem__ and __len__ . """def handleargs(arglist):    """Take list of arguments and extract/create proper start, stop, and step    values and return in a tuple"""    try:        if len(arglist) == 1:            return 0, int(arglist[0]), 1        elif len(arglist) == 2:            return int(arglist[0]), int(arglist[1]), 1        elif len(arglist) == 3:            if arglist[2] == 0:                raise ValueError("step argument must not be zero")            return tuple(int(x) for x in arglist)        else:            raise TypeError("range() accepts 1-3 arguments, given", len(arglist))    except TypeError:        raise TypeError("range() arguments must be numbers or strings "        "representing numbers") def genrange(*a):    """Function to implement 'range' as a generator"""    start, stop, step = handleargs(a)    value = start    while value < stop:        yield value        value += step class oldrange:    """Class implementing a range object.    To the user the instances feel like immutable sequences    (and you can't concatenate or slice them)     Done using the old way (pre-iterators; __len__ and __getitem__) to have an    object be used by a 'for' loop.     """     def __init__(self, *a):        """ Initialize start, stop, and step values along with calculating the        nubmer of values (what __len__ will return) in the range"""        self.start, self.stop, self.step = handleargs(a)        self.len = max(0, (self.stop - self.start) // self.step)     def __repr__(self):        """implement repr(x) which is also used by print"""        return 'range(%r, %r, %r)' % (self.start, self.stop, self.step)     def __len__(self):        """implement len(x)"""        return self.len     def __getitem__(self, i):        """implement x[i]"""        if 0 <= i <= self.len:            return self.start + self.step * i        else:            raise IndexError, 'range[i] index out of range'  def test():    import time, __builtin__    #Just a quick sanity check    correct_result = __builtin__.range(5, 100, 3)    oldrange_result = list(oldrange(5, 100, 3))    genrange_result = list(genrange(5, 100, 3))    if genrange_result != correct_result or oldrange_result != correct_result:        raise Exception("error in implementation:\ncorrect   = %s"                         "\nold-style = %s\ngenerator = %s" %                         (correct_result, oldrange_result, genrange_result))    print "Timings for range(1000):"    t1 = time.time()    for i in oldrange(1000):        pass    t2 = time.time()    for i in genrange(1000):        pass    t3 = time.time()    for i in __builtin__.range(1000):        pass    t4 = time.time()    print t2-t1, 'sec (old-style class)'    print t3-t2, 'sec (generator)'    print t4-t3, 'sec (built-in)'  if __name__ == '__main__':    test()