TypeError when using sorting technique

I am getting a TypeError when I try to use recursion in my merge sort function. I am trying to return a tuple containing a list and a number. If only the list is returned, then my function is able to sort properly and return a sorted list, however.

My desired output:

([1,2,3,4,5,6,7,8,9,10,...],100)

My merge function takes a list and simple lambda expression to compare two numbers.

def merge_s(list_s, ordering):

    if len(list_s) < 2:
        return list_s, 100
    result = []
    mid = int(len(list_s) / 2)
    y = merge_s(list_s[:mid], ordering)
    z = merge_s(list_s[mid:], ordering)
    i = 0
    j = 0
    first_item = ''
    second_item = ''

    while i < len(y) and j < len(z):
        first_item = y[i]
        second_item = z[j]
        if ordering(second_item, first_item):
            result.append(z[j])
            j += 1
        else:
            result.append(y[i])
            i += 1
    result += y[i:]
    result += z[j:]
    return result, 100

My main function:

from random import shuffle
def main():

    for i in range(10):
        data = list(range(100))
        shuffle(data)
        comp = lambda a, b: a < b #my compare function
        (sorted_data, _) = merge_s(data, comp)
        test = (sorted_data,_)
    print(test)

However, I am getting the error:

TypeError: '<' not supported between instances of 'int' and 'list'