I come across what seems like a rather unexpected difference in performance when repeating multiple containers with a custom iterator. I was hoping that someone could help me understand where these differences came from.
First context; I am writing several python extension modules using boost :: python, one of which contains a binding to the three-dimensional vector type float, which implements getitem. Since it has the ability to iterate over it, however it seems rather slow, but it is not clear why I decided to play with some regular python iterators in order to better understand how everything works. That's where these iterators came from ...
class MyIterator1(object):
__slots__ = ['values', 'popfn']
def __init__(self):
self.values = ['x', 'y', 'z']
self.popfn = self.values.pop
def __length_hint__(self):
return 3
def __iter__(self):
return self
def next(self):
try:
return self.popfn()
except IndexError:
raise StopIteration
class MyIterator2(object):
__slots__ = ['values', 'itfn']
def __init__(self):
self.values = ['x', 'y', 'z']
it = iter(self.values)
self.itfn = it.next
def __length_hint__(self):
return 3
def __iter__(self):
return self
def next(self):
return self.itfn()
class MyIterator3(object):
__slots__ = ['values', 'i']
def __init__(self):
self.values = ['x', 'y', 'z']
self.i = 0
def __length_hint__(self):
return 3
def __iter__(self):
return self
def next(self):
if self.i >= 3:
raise StopIteration
value = self.values[self.i]
self.i += 1
return value
def MyIterator4():
val = ['x', 'y', 'z']
yield val[0]
yield val[1]
yield val[2]
script timeit ( , testiter)
import timeit
timer1 = timeit.Timer('r = list(testiter.MyIterator1())', 'import testiter')
timer2 = timeit.Timer('r = list(testiter.MyIterator2())', 'import testiter')
timer3 = timeit.Timer('r = list(testiter.MyIterator3())', 'import testiter')
timer4 = timeit.Timer('r = list(testiter.MyIterator4())', 'import testiter')
timer5 = timeit.Timer('r = list(iter(["x", "y", "z"]))', 'import testiter')
print 'list(testiter.MyIterator1())'
print timer1.timeit()
print "\n"
print 'list(testiter.MyIterator2())'
print timer2.timeit()
print "\n"
print 'list(testiter.MyIterator3())'
print timer3.timeit()
print "\n"
print 'list(testiter.MyIterator4())'
print timer4.timeit()
print "\n"
print 'list(iter(["x", "y", "z"]))'
print timer5.timeit()
list(testiter.MyIterator1())
8.57359290123
list(testiter.MyIterator2())
5.28959393501
list(testiter.MyIterator3())
6.11230111122
list(testiter.MyIterator4())
2.31263613701
list(iter(["x", "y", "z"]))
1.26243281364
, python , . , python. , MyIterator, , , c, . . try/except , , - ?
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