Quesion about the proper use of __slots__

[Steven D'Aprano]

On Mon, 20 Feb 2006 01:14:20 -0800, Zefria wrote:

>>>> class Fighter(object):
> ...     '''Small one man craft that can only harm other fighters on
> their own.'''
> ...     __slots__ = ["fuel","life","armor","weapon","bulk"]
> ...     def __init__(self,statsTuple=(50,5,0,(2,4),1)):
> ...             self.fuel = statsTuple[0]
> ...             self.life = statsTuple[1]
> ...             self.armor = statsTuple[2]
> ...             self.weapon = statsTuple[3]
> ...             self.bulk = statsTuple[4]
> ...
>>>> examp = Fighter()
>>>> examp.rock = 3
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> AttributeError: 'Fighter' object has no attribute 'rock'
>>>>
> 
> Thank you both, I had tried making it a class variable and didn't see
> anything. The trick must have been in making a class that inheriets
> from object.

For technical reasons, __slots__ don't work as expected for old-style
classes, and never will. You have to inherit from object to make them work
correctly.


> Also, I don't generally do any optimization at all yet (as a highschool
> student projects get trashed often enough no to bother over), but in
> this special case I'm expecting each "carrier" to have up to 150
> fighters, and 3 to 5 carriers for each of the two teams, which comes
> out to be quite large.

750 objects is not very many, not unless they are carrying around large
chunks of data. And even then, using __slots__ saves only a small
amount of memory per object.

Write your code the slot-less way, see how it performs, and if it is slow,
change your class definition.



-- 
Steven.