| 1 | """Example of a generator: re-implement the built-in range function
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| 2 | without actually constructing the list of values.
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| 3 |
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| 4 | OldStyleRange is coded in the way required to work in a 'for' loop before
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| 5 | iterators were introduced into the language; using __getitem__ and __len__ .
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| 6 |
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| 7 | """
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| 8 | def handleargs(arglist):
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| 9 | """Take list of arguments and extract/create proper start, stop, and step
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| 10 | values and return in a tuple"""
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| 11 | try:
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| 12 | if len(arglist) == 1:
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| 13 | return 0, int(arglist[0]), 1
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| 14 | elif len(arglist) == 2:
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| 15 | return int(arglist[0]), int(arglist[1]), 1
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| 16 | elif len(arglist) == 3:
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| 17 | if arglist[2] == 0:
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| 18 | raise ValueError("step argument must not be zero")
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| 19 | return tuple(int(x) for x in arglist)
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| 20 | else:
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| 21 | raise TypeError("range() accepts 1-3 arguments, given", len(arglist))
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| 22 | except TypeError:
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| 23 | raise TypeError("range() arguments must be numbers or strings "
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| 24 | "representing numbers")
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| 25 |
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| 26 | def genrange(*a):
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| 27 | """Function to implement 'range' as a generator"""
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| 28 | start, stop, step = handleargs(a)
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| 29 | value = start
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| 30 | while value < stop:
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| 31 | yield value
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| 32 | value += step
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| 33 |
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| 34 | class oldrange:
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| 35 | """Class implementing a range object.
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| 36 | To the user the instances feel like immutable sequences
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| 37 | (and you can't concatenate or slice them)
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| 38 |
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| 39 | Done using the old way (pre-iterators; __len__ and __getitem__) to have an
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| 40 | object be used by a 'for' loop.
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| 41 |
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| 42 | """
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| 43 |
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| 44 | def __init__(self, *a):
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| 45 | """ Initialize start, stop, and step values along with calculating the
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| 46 | nubmer of values (what __len__ will return) in the range"""
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| 47 | self.start, self.stop, self.step = handleargs(a)
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| 48 | self.len = max(0, (self.stop - self.start) // self.step)
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| 49 |
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| 50 | def __repr__(self):
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| 51 | """implement repr(x) which is also used by print"""
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| 52 | return 'range(%r, %r, %r)' % (self.start, self.stop, self.step)
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| 53 |
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| 54 | def __len__(self):
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| 55 | """implement len(x)"""
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| 56 | return self.len
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| 57 |
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| 58 | def __getitem__(self, i):
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| 59 | """implement x[i]"""
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| 60 | if 0 <= i <= self.len:
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| 61 | return self.start + self.step * i
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| 62 | else:
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| 63 | raise IndexError, 'range[i] index out of range'
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| 64 |
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| 65 |
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| 66 | def test():
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| 67 | import time, __builtin__
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| 68 | #Just a quick sanity check
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| 69 | correct_result = __builtin__.range(5, 100, 3)
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| 70 | oldrange_result = list(oldrange(5, 100, 3))
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| 71 | genrange_result = list(genrange(5, 100, 3))
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| 72 | if genrange_result != correct_result or oldrange_result != correct_result:
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| 73 | raise Exception("error in implementation:\ncorrect = %s"
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| 74 | "\nold-style = %s\ngenerator = %s" %
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| 75 | (correct_result, oldrange_result, genrange_result))
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| 76 | print "Timings for range(1000):"
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| 77 | t1 = time.time()
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| 78 | for i in oldrange(1000):
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| 79 | pass
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| 80 | t2 = time.time()
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| 81 | for i in genrange(1000):
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| 82 | pass
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| 83 | t3 = time.time()
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| 84 | for i in __builtin__.range(1000):
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| 85 | pass
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| 86 | t4 = time.time()
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| 87 | print t2-t1, 'sec (old-style class)'
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| 88 | print t3-t2, 'sec (generator)'
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| 89 | print t4-t3, 'sec (built-in)'
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| 90 |
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| 91 |
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| 92 | if __name__ == '__main__':
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| 93 | test()
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