[Python-ideas] caching properties

[George Sakkis]

On Thu, Apr 30, 2009 at 7:37 PM, Ben Finney <ben+python at benfinney.id.au> wrote:

> George Sakkis <george.sakkis at gmail.com>
> writes:
>
>> I think It's clear by now that caching in the general case is not
>> trivial, both in terms of API and implementation. That makes the
>> original request - caching properties only - more appealing since most
>> problems go away if there are no parameters.
>
> Nevertheless, the “memoize” pattern *is* well-understood, and already
> implemented for Python as discussed earlier. It covers the “cached
> property” as a degenerate (i.e. simpler) case. Making a specific
> decorator that *only* addresses “cached property” is too narrow, IMO.
>
> I think a “memoize” decorator (by whatever name) is the right level of
> generality to address this use case, and has the advantage of existing
> implementations.

IMHO no existing implementation is good enough for addition to the
standard library. Off the top of my head, some of the issues a general
and robust implementation should address are:
- Non hashable parameters.
- Caching keys based on a subset of the provided parameters (or
perhaps more general a key function).
- Bounded-length caches.
- Different expiration policies for bounded-length caches.
- As good performance as possible given the previous constraints.

Of course one can write a vanilla version in a few lines, and indeed
searching for "memoize" in code.activestate.com returns no less than
125 results (including one I posted 4.5 years ago). I think the sheer
number of the posted recipes is an indication that none of them has
"solved" the problem for good, otherwise people would just reuse it
instead of keep posting alternatives.

George