[openstack-dev] [all][python3] use of six.iteritems()

John Dennis jdennis at redhat.com
Thu Jun 11 18:45:02 UTC 2015

On 06/11/2015 01:46 PM, Mike Bayer wrote:
> I am firmly in the "let's use items()" camp.  A 100 ms difference for 
> a totally not-real-world case of a dictionary 1M items in size is no 
> kind of rationale for the Openstack project - if someone has a 
> dictionary that's 1M objects in size, or even 100K, that's a bug in 
> and of itself.
> the real benchmarks we should be using, if we are to even bother at 
> all (which we shouldn't), is to observe if items() vs. iteritems() has 
> *any* difference that is at all measurable in terms of the overall 
> execution of real-world openstack use cases.   These nano-differences 
> in speed are immediately dwarfed by all those operations surrounding 
> them long before we even get to the level of RPC overhead.

Lessons learned in the trenches:

* The best code is the simplest [1] and easiest to read.

* Code is write-once, read-many; clarity is a vital part of the read-many.

* Do not optimize until functionality is complete.

* Optimize only after profiling real world use cases.

* Prior assumptions about what needs optimization are almost always 
proven wrong by a profiler.

* I/O latency vastly overwhelms most code optimization making obtuse 
optimization pointless and detrimental to long term robustness.

* The amount of optimization needed is usually minimal, restricted to 
just a few code locations and 80% of the speed increases occur in just 
the first few tweaks after analyzing profile data.

[1] Compilers can optimize simple code best, simple code is easy to 
write and easier to read while at the same time giving the tool chain 
the best chance of turning your simple code into efficient code. (Not 
sure how much this applies to Python, but it's certainly true of other 
compiled languages.)


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