[SciPy-User] caching function values

nicky van foreest vanforeest@gmail....
Mon Mar 15 03:12:02 CDT 2010


Hi Ralf and Paul,

Thanks for sharing your ideas.

Nicky

On 14 March 2010 04:21, Paul Anton Letnes <paul.anton.letnes@gmail.com> wrote:
> On 13. mars 2010, at 13.06, nicky van foreest wrote:
>
>> Hi,
>>
>> When calling a function for the first time I like to cache some
>> complicated computations (that only have to be done once), and then
>> use this cached stuff in all subsequent calls to the functions. I came
>> across the following trick on the net:
>>
>> def dummy(x, firstTime = [1]):
>>    if firstTime[0] == 1:
>>        A = 3  # typically some lengthy do-once computation to obtain a matrix A
>>        dummy.A = A # store it
>>        firstTime[0] = 0 # ensure this piece of code will not be run again
>>    u = dummy.A*x  # use the cached value of A in the real computations
>>    return u
>>
>> Are there other (less tricky) ways to achieve the same effect, without
>> using a class? (As far as I can see, using classes would involve some
>> extra lines of code, for instance, I have to instantiate it.)
>>
>> Thanks for any advice.
>>
>> Nicky
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>
> How about just making the following class?
>
> class DummyClass(object):
>        def __init__():
>                self.A = lengthy_calculation()
>        def __call__(self, x):
>                return self.A *x
>
> Somewhere else, type
> dummy = DummyClass()
> y = dummy(x) # or whatever
>
> I'd say that this is as readable, and in fact, not noticeably longer.
>
> Paul
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>


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