+++ /dev/null
-"""Example of a generator: re-implement the built-in range function\r
-without actually constructing the list of values.\r
-\r
-OldStyleRange is coded in the way required to work in a 'for' loop before\r
-iterators were introduced into the language; using __getitem__ and __len__ .\r
-\r
-"""\r
-def handleargs(arglist):\r
- """Take list of arguments and extract/create proper start, stop, and step\r
- values and return in a tuple"""\r
- try:\r
- if len(arglist) == 1:\r
- return 0, int(arglist[0]), 1\r
- elif len(arglist) == 2:\r
- return int(arglist[0]), int(arglist[1]), 1\r
- elif len(arglist) == 3:\r
- if arglist[2] == 0:\r
- raise ValueError("step argument must not be zero")\r
- return tuple(int(x) for x in arglist)\r
- else:\r
- raise TypeError("range() accepts 1-3 arguments, given", len(arglist))\r
- except TypeError:\r
- raise TypeError("range() arguments must be numbers or strings "\r
- "representing numbers")\r
-\r
-def genrange(*a):\r
- """Function to implement 'range' as a generator"""\r
- start, stop, step = handleargs(a)\r
- value = start\r
- while value < stop:\r
- yield value\r
- value += step\r
-\r
-class oldrange:\r
- """Class implementing a range object.\r
- To the user the instances feel like immutable sequences\r
- (and you can't concatenate or slice them)\r
-\r
- Done using the old way (pre-iterators; __len__ and __getitem__) to have an\r
- object be used by a 'for' loop.\r
-\r
- """\r
-\r
- def __init__(self, *a):\r
- """ Initialize start, stop, and step values along with calculating the\r
- nubmer of values (what __len__ will return) in the range"""\r
- self.start, self.stop, self.step = handleargs(a)\r
- self.len = max(0, (self.stop - self.start) // self.step)\r
-\r
- def __repr__(self):\r
- """implement repr(x) which is also used by print"""\r
- return 'range(%r, %r, %r)' % (self.start, self.stop, self.step)\r
-\r
- def __len__(self):\r
- """implement len(x)"""\r
- return self.len\r
-\r
- def __getitem__(self, i):\r
- """implement x[i]"""\r
- if 0 <= i <= self.len:\r
- return self.start + self.step * i\r
- else:\r
- raise IndexError, 'range[i] index out of range'\r
-\r
-\r
-def test():\r
- import time, __builtin__\r
- #Just a quick sanity check\r
- correct_result = __builtin__.range(5, 100, 3)\r
- oldrange_result = list(oldrange(5, 100, 3))\r
- genrange_result = list(genrange(5, 100, 3))\r
- if genrange_result != correct_result or oldrange_result != correct_result:\r
- raise Exception("error in implementation:\ncorrect = %s"\r
- "\nold-style = %s\ngenerator = %s" %\r
- (correct_result, oldrange_result, genrange_result))\r
- print "Timings for range(1000):"\r
- t1 = time.time()\r
- for i in oldrange(1000):\r
- pass\r
- t2 = time.time()\r
- for i in genrange(1000):\r
- pass\r
- t3 = time.time()\r
- for i in __builtin__.range(1000):\r
- pass\r
- t4 = time.time()\r
- print t2-t1, 'sec (old-style class)'\r
- print t3-t2, 'sec (generator)'\r
- print t4-t3, 'sec (built-in)'\r
-\r
-\r
-if __name__ == '__main__':\r
- test()\r