random.py 文件源码

def randrange(self, *args):
        """randrange([start,] stop[, step]):
        Return a randomly-selected element from range(start, stop, step)."""
        if len(args) == 3:
            (start, stop, step) = args
        elif len(args) == 2:
            (start, stop) = args
            step = 1
        elif len(args) == 1:
            (stop,) = args
            start = 0
            step = 1
        else:
            raise TypeError("randrange expected at most 3 arguments, got %d" % (len(args),))
        if (not isinstance(start, (int, long))
                or not isinstance(stop, (int, long))
                or not isinstance(step, (int, long))):
            raise TypeError("randrange requires integer arguments")
        if step == 0:
            raise ValueError("randrange step argument must not be zero")

        num_choices = ceil_div(stop - start, step)
        if num_choices < 0:
            num_choices = 0
        if num_choices < 1:
            raise ValueError("empty range for randrange(%r, %r, %r)" % (start, stop, step))

        # Pick a random number in the range of possible numbers
        r = num_choices
        while r >= num_choices:
            r = self.getrandbits(size(num_choices))

        return start + (step * r)