On 8/1/2017 7:06 AM, Matt Wheeler wrote:
On Tue, 1 Aug 2017 at 02:32 Terry Reedy <tjre...@udel.edu> wrote:
On 7/31/2017 7:31 PM, t...@tomforb.es wrote:
As part of the Python 3 cleanup in Django there are a fair few uses of
@functools.lru_cache on functions that take no arguments.
This makes no sense to me. If the function is being called for
side-effects, then it should not be cached. If the function is being
called for a result, different for each call, calculated from a changing
environment, then it should not be cached. (Input from disk is an
example.) If the function returns a random number, or a non-constant
value from an oracle (such as a person), it should not be cached. If
the function returns a constant (possible calculated once), then the
constant should just be bound to a name (which is a form of caching)
rather than using the overkill of an lru cache. What possibility am I
missing?
A function which is moderately expensive to run, that will always return
the same result if run again in the same process, and which will not be
needed in every session.
In initialization section:
answer = None
Somewhere else:
answer = expensive_calculaton() if answer is None else answer
The conditional has to be cheaper than accessing lru cache. There can
be more than one of these.
--
Terry Jan Reedy
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