[SciPy-User] caching function values

[Paul Anton Letnes]

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