On 2010-04-02 20:24:46 -0700, Patrick Maupin said:
On Apr 2, 10:11 pm, Stephen Hansen <apt.shan...@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.
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