Problem of Readability of Python

[Alex Martelli]

Licheng Fang <fanglicheng at gmail.com> wrote:
   ...
> Python Tutorial says an empty class can be used to do this. But if
> namespaces are implemented as dicts, wouldn't it incur much overhead
> if one defines empty classes as such for some very frequently used
> data structures of the program?

Just measure:

$ python -mtimeit -s'class A(object):pass' -s'a=A()' 'a.zop=23'
1000000 loops, best of 3: 0.241 usec per loop

$ python -mtimeit -s'a=[None]' 'a[0]=23'
10000000 loops, best of 3: 0.156 usec per loop

So, the difference, on my 18-months-old laptop, is about 85 nanoseconds
per write-access; if you have a million such accesses in a typical run
of your program, it will slow the program down by about 85 milliseconds.
Is that "much overhead"?  If your program does nothing else except those
accesses, maybe, but then why are your writing that program AT ALL?-)

And yes, you CAN save about 1/3 of those 85 nanoseconds by having
'__slots__=["zop"]' in your class A(object)... but that's the kind of
thing one normally does only to tiny parts of one's program that have
been identified by profiling as dramatic bottlenecks, to shave off the
last few nanoseconds in the very last stages of micro-optimization of a
program that's ALMOST, but not QUITE, fast enough... knowing about such
"extreme last-ditch optimization tricks" is of very doubtful value (and
I think I'm qualified to say that, since I _do_ know many of them...:-).
There ARE important performance things to know about Python, but those
worth a few nanoseconds don't matter much.


Alex