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Python saving an eval function

Say I have a function fun(f, x, y) where x and y are numbers and f is a string specifying a function such as "1 / x ** 2 + y".

I wish to use this function f a lot, say a few million times, and the values of x and y change between each use.
Therefore calling eval(f) takes a significant amount of time as opposed to just calculating the value of the function each time. (About 50x, in my measured case.)

Is there any way to save this function f so that I would only have to call eval once?

PS. Please do not discuss the (un)safety of using eval here, I am aware of it, but this code isn't going anywhere where a 3rd party will run it, nor is it relevant to my question.

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Torn Avatar asked May 04 '17 08:05

Torn


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1 Answers

You could eval the lambda, so you just evaluate it once, and after that it's a function that you can use:

s = "1 / x ** 2 + y"

s = "lambda x,y: "+s
f = eval(s)
x = 2
y = 3
print(f(x,y))

I get 3.25, but I can change x and y as many times I need without evaluating the expression again.

like image 109
Jean-François Fabre Avatar answered Oct 01 '22 07:10

Jean-François Fabre