73 lines
1.7 KiB
Python
73 lines
1.7 KiB
Python
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# Example of a generator: re-implement the built-in range function
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# without actually constructing the list of values. (It turns out
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# that the built-in function is about 20 times faster -- that's why
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# it's built-in. :-)
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# Wrapper function to emulate the complicated range() arguments
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def range(*a):
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if len(a) == 1:
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start, stop, step = 0, a[0], 1
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elif len(a) == 2:
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start, stop = a
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step = 1
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elif len(a) == 3:
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start, stop, step = a
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else:
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raise TypeError, 'range() needs 1-3 arguments'
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return Range().init(start, stop, step)
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# Class implementing a range object.
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# To the user the instances feel like immutable sequences
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# (and you can't concatenate or slice them)
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class Range:
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# initialization -- should be called only by range() above
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def init(self, start, stop, step):
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if step == 0:
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raise ValueError, 'range() called with zero step'
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self.start = start
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self.stop = stop
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self.step = step
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self.len = max(0, int((self.stop - self.start) / self.step))
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return self
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# implement `x` and is also used by print x
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def __repr__(self):
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return 'range' + `self.start, self.stop, self.step`
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# implement len(x)
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def __len__(self):
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return self.len
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# implement x[i]
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def __getitem__(self, i):
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if 0 <= i < self.len:
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return self.start + self.step * i
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else:
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raise IndexError, 'range[i] index out of range'
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# Small test program
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def test():
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import time, builtin
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print range(10), range(-10, 10), range(0, 10, 2)
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for i in range(100, -100, -10): print i,
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print
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t1 = time.millitimer()
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for i in range(1000):
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pass
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t2 = time.millitimer()
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for i in builtin.range(1000):
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pass
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t3 = time.millitimer()
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print t2-t1, 'msec (class)'
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print t3-t2, 'msec (built-in)'
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test()
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