On 2019-01-19 00:28, Greg Ewing wrote:
Tim Peters wrote:
The dict itself keeps the objects alive.
Yes, but the idea of a cache is that you're free to flush
things out of it to make room for something else without
breaking anything.
It sounds like MRAB is using ids as weak references,
without the assurance actual weak references give you
that they become invalidated when the refefenced object
goes away,
"Cache" was the wrong word for what it does. I'm not using the id as a
weak reference.
Sometimes I might want to store a collection of objects and their order
isn't important. I can add an object to the collection, or remove an
object from it.
If I used a list, adding would be quick, but removing would require
searching the list.
By putting them in a dict, keyed by the id, I can remove an object in O(1).
Trust me, I'm not doing anything that's unreliable! (And I _have_ done
programming in C with the Python API, so I know all about refcounts...) :-)
No such uses care about object addresses, though - just that id(obj)
returns a value usable as a dict key, unique among all reachable
objects at the time `id()` is called.
Yep. In hindsight it was probably a mistake for the docs
to talk about addresses in relation to id() -- it seems to
have given some people unrealistic expectations.
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