Kako se lotit case insensitive "find and replace"?

import re;

string_in = "Set manjših pravokotnih vakuumskih posod, 5-delni set";

print("string_in=" + string_in);

input = "set delni vakuum kot delni";

print("input=" + input);

string_out = "";

items = [];

items = input.split(" ");

items = sorted(items, key=len, reverse=True);

items = list(dict.fromkeys(items));

print("items=" + str(items));

string_items = string_in.split(" ");

for i in range(0, len(string_items)):

    found = False;

    for j in range(0, len(items)):

        match = re.search(items[j].lower(), string_items[i].lower());

        if match != None:

            string_out = string_out + string_items[i][0:match.start()] + "<span>" + string_items[i][match.start():match.end()] + "</span>" + string_items[i][match.end():] + " ";

            found = True;
            break;

    if found == False:

        string_out = string_out + string_items[i] + " ";

string_out = string_out.strip();

print("string_out=" + string_out);

string_in=Set manjših pravokotnih vakuumskih posod, 5-delni set
input=set delni vakuum kot delni
items=['vakuum', 'delni', 'set', 'kot']
string_out=<span>Set</span> manjših pravo<span>kot</span>nih <span>vakuum</span>skih posod, 5-<span>delni</span> <span>set</span>

def make_it_happen(input_string, search_query):

    # set output
    output_string = "";

    # split search_query by space
    search_query_items_temp = search_query.split(" ");

    # order search query items by string length from longest to shortest
    search_query_items_temp = sorted(search_query_items_temp, key=len, reverse=True);

    # remove duplicates
    search_query_items_temp = list(dict.fromkeys(search_query_items_temp));

    # make empty list for final search query items
    search_query_items_final = [];

    # go throug search query items and make sure to not add string with length 0
    for i in range(0, len(search_query_items_temp)):

        if len(search_query_items_temp[i]) > 0:
            search_query_items_final.append(search_query_items_temp[i]);

    # split input string by space
    input_string_items = input_string.split(" ");

    # go for each input string item
    for i in range(0, len(input_string_items)):

        found = False;

        # go trhoug each search query item
        for j in range(0, len(search_query_items_final)):

            match = re.search(search_query_items_final[j].lower(), input_string_items[i].lower());

            # if there is match
            if match != None:

                output_string = output_string + input_string_items[i][0:match.start()] + "<span>" + \
                         input_string_items[i][match.start():match.end()] + "</span>" + \
                         input_string_items[i][match.end():] + " ";

                # set found to true and break
                found = True;
                break;

        if found == False:

            # if not found just append input item to output item
            output_string = output_string + input_string_items[i] + " ";

    # strip spaces
    output_string = output_string.strip();

    # return output
    return output_string;