It's ok to __slots__ for what they were intended

[Fredrik Lundh]

John Nagle wrote:

>      I'd like to hear more about what kind of performance gain can be
> obtained from "__slots__".  I'm looking into ways of speeding up
> HTML parsing via BeautifulSoup.  If a significant speedup can be
> obtained when navigating large trees of small objects, that's worth
> quite a bit to me.

The following micro-benchmarks are from Python 2.5 on a Core Duo 
machine.  C0 is an old-style class, C1 is a new-style class, C2 is a 
new-style class using __slots__:

# read access
$ timeit -s "import q; o = q.C0(); o.attrib = 1" "o.attrib"
10000000 loops, best of 3: 0.133 usec per loop
$ timeit -s "import q; o = q.C1(); o.attrib = 1" "o.attrib"
10000000 loops, best of 3: 0.184 usec per loop
$ timeit -s "import q; o = q.C2(); o.attrib = 1" "o.attrib"
10000000 loops, best of 3: 0.161 usec per loop

# write access
$ timeit -s "import q; o = q.C0(); o.attrib = 1" "o.attrib = 1"
10000000 loops, best of 3: 0.15 usec per loop
$ timeit -s "import q; o = q.C1(); o.attrib = 1" "o.attrib = 1"
1000000 loops, best of 3: 0.217 usec per loop
$ timeit -s "import q; o = q.C2(); o.attrib = 1" "o.attrib = 1"
1000000 loops, best of 3: 0.209 usec per loop

$ more q.py
class C0:
     pass

class C1(object):
     pass

class C2(object):
     __slots__ = ["attrib"]

Your mileage may vary.

 > I'm looking into ways of speeding up HTML parsing via BeautifulSoup.

The solution to that is spelled "lxml".

</F>