__slots__

[Duncan Booth]

Ron Garret wrote:

>  aleaxit at yahoo.com (Alex Martelli) wrote:
> 
>> > One other question I did not get answered:  is there any
>> > simple example of a Pythonic use of __slots__ that does NOT
>> > involve the creation of **many** instances.
>> 
>> Since the only benefit of __slots__ is saving a few bytes per instance,
>> it's not worth the bother unless there are many instances -- so, the
>> answer is 'no'.
> 
> I can think of at least two other benefits to using __slots__:
> 
> 1.  If you have a typo in an attribute assignment you get an exception 
> instead of a latent downstream bug.

Only if all classes in the inheritance define __slots__, and don't include 
__dict__ in their slots. In particular, it means you can never rely on 
this in any code you write which inherits from a library class over which 
you have no control.

In other words, it is such a risky thing to depend on that you would be 
much better never to rely on it. Try writing some unit tests instead.

> 
> 2.  Implicit documentation.

Explicit is better than implicit.