Open Stack

On Thu, Jun 11, 2015 at 8:33 AM, Sean Dague <sean at dague.net> wrote:
> On 06/11/2015 09:02 AM, Jay Pipes wrote:
>> On 06/11/2015 01:16 AM, Robert Collins wrote:
>>> But again - where in OpenStack does this matter the slightest?
>>
>> Precisely. I can't think of a single case where we are iterating over
>> anywhere near the number of dictionary items that we would see any
>> impact whatsoever.

In neutron, the ovsdb native code iterates over fairly large
dictionaries since the underlying OVS library stores OVSDB tables
completely in memory as dicts. I just looked at the code I wrote and
it currently uses values() and I now want to switch it to
six.itervalues() :p.

>> Best,
>> -jay
>
> +1.
>
> This is a massive premature optimization which just makes all the code
> gorpy for no real reason.

Premature optimization is about wasting a bunch of time trying to
optimize code before you know you need to, not about following the
accepted almost-always-faster/always-less-memory-using solution that
already exists. Memory-wise it's the difference between a constant
88-byte iterator and the storage for an additional list of tuples. And
if Raymond Hettinger, in a talk called "Transforming Code Into
Beautiful Idiomatic Python" specifically mentions that people should
always use iteritems
(https://www.youtube.com/watch?v=OSGv2VnC0go&feature=youtu.be&t=21m24s),
I tend to believe him. Sure, it'd be much better if Python 3 and
Python 2 both returned iterators for items(), values(), keys(), etc.,
but it doesn't. Wasting memory for purely aesthetic reasons (they're
even both the same number of lines) is just a bad idea, IMNSHO.

Terry