试写Python内建函数range()

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 class my_range(object):

     def __init__(self, *args):
         if not args:
             raise TypeError, 'range expected at least 1 arguments, got 0'
         elif len(args) == 1:
             self.start, self.stop, self.step = (0, args[0], 1)
         elif len(args) == 2:
             self.start, self.stop, self.step = (args[0], args[1], 1)
         elif len(args) == 3:
             self.start, self.stop, self.step = args
         else:
             raise TypeError, 'range expected at most 3 arguments, got %d' % len(args)
         self.n = 0

     def next(self):
         while True:
             r = self.start + self.step * self.n
             if r >= self.stop:
                 break
             self.n += 1
             return r
         raise StopIteration

     def __iter__(self):
         return self