C-style static variables in Python?

[Stephen Hansen]

On 2010-04-02 20:24:46 -0700, Patrick Maupin said:

> On Apr 2, 10:11 pm, Stephen Hansen <apt.shan... at gmail.invalid> wrote:
>> 
>> I don't know if properties are really faster or slower then a
>> __getattr__, but I find them a lot cleaner if I want to delay some
>> calculation until needed like that.
> 
> Well, the relative speed of properties vs. __getattr__ can become
> irrelevant in at least two ways:
> 
> 1) If the __getattr__ only calculates the value one time and then
> stuffs it into the instance dictionary, now you are really comparing
> the relative speed of properties vs. lookup of an attribute in the
> instance dict.  If you're at all concerned about speed, I think there
> is a clear winner here.

I concede it would probably be notably faster, but there's a big 
difference between "at all concerned about speed" and "optimizing a 
profiled bottleneck".

The speed difference between direct attribute lookup and properties may 
be notable, but that doesn't make a clear winner here. Now that I have 
(with either method) optimized the expensive value-calculation 
operation such that it only happens on-demand and once, I now have to 
weigh further optimization.

Is the difference in speed between a standard attribute lookup and a 
property fetch worth losing the clarity the property brings over the 
__getattr__ solution, especially considering the __getattr__ creates a 
fuzzy 'sometimes this code is responsible, othertimes the dict is' 
situation that someone may down the road miss in maintenance?

For me, usually not-- unless profiling pushes me to reconsider. But 
everyone makes these calls differently.

> 2) There is a single __getattr__ function, vs. one property for every
> attribute that needs a property.  In cases where you can somehow
> easily compute the attribute names as well as the attribute values,
> __getattr__ can be a *lot* less code than defining dozens of
> properties.

I don't really mind a lot of properties, if they're simple. Then again, 
I often prefer regular ol' attributes where possible :) However, if I'm 
doing a dispatching sort of mechanism, or a situation where the "name" 
isn't something static, set in stone or pre-defined-- then certainly, 
__getattr__ is a fine solution. I don't mind it where its the clearest 
way to accomplish a goal.

-- 
--S

... p.s: change the ".invalid" to ".com" in email address to reply privately.