Python: passing arguments to a function

Question

I am using dlib's find_min_global function, an optimization algorithm which helps to find values which minimize the output of a function. For example

import dlib
def holder_table(x0,x1):
    return -abs(sin(x0)*cos(x1)*exp(abs(1-sqrt(x0*x0+x1*x1)/pi)))

x,y = dlib.find_min_global(holder_table, 
                           [-10,-10],  # Lower bound constraints on x0 and x1 respectively
                           [10,10],    # Upper bound constraints on x0 and x1 respectively
                           80)         # The number of times find_min_global() will call holder_table()

Here the holder_table function returns the value that needs to be minimized for different values of x0 and x1.

Here the holder_table function takes in only the values that need to be optimized that is x0 and x1. But the function that I want to use with the dlib function takes more than x0 and x1. The function definiton looks like so

def holder_table(a,b,x0,x1):
    return -abs(sin(b*x0/a)*cos(x1)*exp(abs(1-sqrt(x0*x0+x1*x1)/pi)))

The values a, b are not fixed and are the outputs of another function. Now, I can directly call the function the returns a, b inside the holder_table but I dont want to end up re-calculating them because each time holder_table is called a, b gets re-calculated and the process is time consuming.

How do I pass a, b to the holder_table function?

Answer 1

Your question is not 100% clear but it looks like you want a partial application. In Python this can be done using the dedicated functools.partial object, or quite simply with a closure (using either an inner function or lambda)

def holder_table(a,b,x0,x1):
    return -abs(sin(b*x0/a)*cos(x1)*exp(abs(1-sqrt(x0*x0+x1*x1)/pi)))


def main():
    a, b = some_heavy_function(...)
    holder_table_partial = lambda ax, ay: holder_table(a, b, ax, ay)
    x, y = dlib.find_min_global(
        holder_table_partial, [-10,-10], [10,10], 80
        )