[Python-Dev] Replacing self.__dict__ in __init__

[Raymond Hettinger]

> On Mar 24, 2018, at 7:18 AM, Tin Tvrtković <tinchester at gmail.com> wrote:
> 
> it's faster to do this:
> 
>     self.__dict__ = {'a': a, 'b': b, 'c': c}
> 
> i.e. to replace the instance dictionary altogether. On PyPy, their core devs inform me this is a bad idea because the instance dictionary is special there, so we won't be doing this on PyPy. 
> 
> But is it safe to do on CPython?

This should work. I've seen it done in other production tools without any ill effect.

The dict can be replaced during __init__() and still get benefits of key-sharing.  That benefit is lost only when the instance dict keys are modified downstream from __init__().  So, from a dict size point of view, your optimization is fine.

Still, you should look at whether this would affect static type checkers, lint tools, and other tooling.


Raymond