[EMAIL PROTECTED] wrote:
> I have a class for rectangle and it has two points in its __slots__ .
> However, we can derive a number of properties like width, height,
> centerPoint etc from these two points. Now, I want to be able to set
> and get these properties directly from the instances. I can either def
> __setattr__ , __getattr__
But this won't help with introspection...
> or I can define function for each property
> like setWidth(), setHeight() . Which one would be faster?
You mean faster performances or faster to implement ?
> I would
> prefer doing through __setattr__, __getattr__ because it makes the code
> more readable.
You mean the client code ?
> However, speed is a concern I would have to do these operations in few
> thousand iterations for about 50-100 rectangles.
>
The canonical solution is to use either properties or custom
descriptors[1]. Custom descriptors should be a bit faster than
properties (since you save a couple function calls), but I have not done
any benchmark... It should also be a bit faster than __getattr__, which
is only used as a fallback when all other lookup rules have failed (here
again, don't take me on words and do some benchmarking). As a last
point, descriptors show up as class and instance attributes, which helps
with introspection.
class Height(object):
def __get__(self, instance, cls):
if instance is None: return self
return instance.bottomright.y - instance.topleft.y
def __set__(self, instance, value):
instance.bottomright.y = instance.topleft.y + value
class Width(object):
def __get__(self, instance, cls):
if instance is None: return self
return instance.bottomright.x - instance.topleft.x
def __set__(self, instance, value):
instance.bottomright.x = instance.topleft.x + value
class Rectangle(object):
def __init__(self):
self.topleft = Point(10, 10)
self.bottomright = Point(20, 30)
height = Height()
width = Width()
r = Rectangle()
r.with = 40
(not tested)
[1] :
* http://docs.python.org/ref/descriptors.html
* http://users.rcn.com/python/download/Descriptor.htm
My 2 cents...
--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in '[EMAIL PROTECTED]'.split('@')])"
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