Approximate resistor value "target" by using at most "max_resistors" from a given list of resistor values

resistor.py

import itertools
import sys
from fractions import Fraction

def split_integer(n):
    for a in range(1, 1 + n // 2):
        yield a, n - a

def resistor_pairs(n, cur_list):
    for a, b in split_integer(n):
        yield from itertools.product(cur_list[a], cur_list[b])
            
def series():
    return (lambda a, b: a + b, lambda a, b: "(%s + %s)" % (a, b))

def parallel():
    return (lambda a, b: a * b / (a + b), lambda a, b: "(%s // %s)" % (a, b))

def min_resistor(target, max_resistor, resistor_list):
    cur_list = {1: [(Fraction(r), str(r)) for r in resistor_list]}
    values = set(Fraction(r) for r in resistor_list)
    cur_diff = 1e18
    cur_value = 1e18
    cur_str = ""
    for n in range(2, 1 + max_resistor):
        new_list = []
        for r1, r2 in resistor_pairs(n, cur_list):
            for val_op, str_op in [series(), parallel()]:
                new_value = val_op(r1[0], r2[0])
                new_str = str_op(r1[1], r2[1]) 
                if new_value not in values:
                    new_list.append((new_value, new_str))
                    values.add(new_value)
                    diff = abs(new_value - target)
                    if diff < cur_diff:
                        cur_diff = diff
                        cur_str = new_str
                        cur_value = new_value
        cur_list[n] = new_list
    print(float(cur_value), cur_str)                

def main():
    if len(sys.argv) < 3:
        print("Usage: python3 resistor.py target max_resistors R1 R2 R3 ...")
        return 
    min_resistor(float(sys.argv[1]), int(sys.argv[2]), map(int, sys.argv[3:]))

if __name__ == '__main__':
    main()