How Not to write multi-threaded python code

factorial.py

import _thread
from time import sleep

def fmap(out, a, b): out.append(a * b)
    
def threading(pairs):
    out = []
    for (a, b) in pairs:
        thread = _thread.start_new_thread(fmap, (out, a, b, ))
    return out

def make_pairs(a):
    if len(a) % 2 != 0:
        a.append(1)
    pairs = []
    for i in range(0, len(a), 2):
        pairs.append((a[i], a[i+1]))
    return pairs

def factorial(N):
    
    pairs = make_pairs([x for x in range(1, N + 1)])

    while len(pairs) != 1:
        out = threading(pairs)
        while len(out) != len(pairs):
            sleep(0.01)

        pairs = make_pairs(out)
        print(pairs)
        
    return pairs[0][0] * pairs[0][1]

if __name__ == '__main__':
    print(factorial(10))

    

text_search.py

import _thread
from time import sleep

def slice(text, chunk_size):
    chunks = []
    for i in range(0, len(text), chunk_size):
        chunks.append(text[i:i+chunk_size])
    return chunks


def count_letters(text, letter, threads):
    TOTALS = []
    
    def count_chunk(chunk, letter):
        TOTALS.append(sum([c == letter for c in chunk]))
            
    length = len(text)
    chunk_size = length // threads
    chunks = slice(text, chunk_size)

    for chunk in chunks:
        _thread.start_new_thread(count_chunk, (chunk, letter, ))
    
    while len(TOTALS) != len(chunks):
        sleep(0.01)
    
    return sum(TOTALS)
    
if __name__ == '__main__':
    print(count_letters("there are so many letter e here", "e", 8))