I am writing a python program to find and return a list of Twin primes between two numbers.

This is my code:

#prime selector
def is_prime(num): #Determines whether a number is prime by checking divisibility up to its square root.
    # any num less that 2 is not a prime
    if num < 2: 
        return False
    # 2 is a special case, the only even prime number
    if num == 2: 
        return True
    # even numbers > 2 are not primes
    if num % 2 == 0: 
        return False
    upr_lmt = int((num ** 0.5) + 1) 
    # only need to check divisors up to the square root of given number
    for number in range(3, upr_lmt, 2): 
    # Check only odd numbers starting from 3
        if num % number == 0:
            return False
    return True


def primeLister(end_point, st_point = 2):#Generates a list of prime numbers between st_point and end_point.
    primeList = []
    for i in range(st_point, end_point + 1):
        if is_prime(i):
            primeList.append(i)
    return primeList

def Twin_Primes(a, b): #Finds and returns a list of twin primes between a and b, with each pair listed in ascending order.
    prime_list = primeLister(b, a)
    size = len(prime_list)
    twin_prime_list = []
    for i in range(size - 1):
        num1, num2 = prime_list[i], prime_list[i + 1]
        if num2 - num1 == 2:
            twin_prime = (num1, num2)
            twin_prime_list.append(twin_prime)
    if len(twin_prime_list) == 0:
        return ["<NONE>"]
    return twin_prime_list

It is saved as prime_selector.py in a folder.

This is the testcase that I have written:

# Test case
from prime_selector import is_prime
from prime_selector import primeLister
from prime_selector import Twin_Primes
import time
import os
import threading


def measure_time():
    return time.perf_counter()

def log_newline(file_writer):
    file_writer.write("nn")

def log_testcase(case_num, case_desc, result, file_writer):
    file_writer.write(f"================= Test Case {case_num + 1} =================n")
    print((f"================= Test Case {case_num + 1} ================="))
    file_writer.write(case_desc)
    print(case_desc, end = "")
    file_writer.write(result)
    print(result)

def log_time(case_num, duration, file_writer):
    file_writer.write(f"Time taken for Test Case {case_num + 1} : {duration:.10f} seconds")
    print(f"Time taken for Test Case {case_num + 1} : {duration:.10f} seconds")

def clear_screen():
    #time.sleep(30)
    if os.name == 'nt':
        _ = os.system('cls')
    else:
        _ = os.system('clear')

def long_running_task():
    while True:
        main_start_time = measure_time()
        num_list = [2,3,5,7,9,15,24,4,13,90,17,27,19,100,99991,999999937,1,10]
        #num_list.remove(999999937)

        # Start of testing for is_prime()
        with open("./is_prime_testcase","w") as file_writer:

            for case_num, i in enumerate(num_list):
                sub_time_start = measure_time()

                case_desc = f"Is {i} a Prime Number?n"
                result = f" > Yes, it is.n" if is_prime(i) else f" > No, it is not.n"

                log_testcase(case_num,case_desc,result,file_writer)

                duration = measure_time() - sub_time_start
                log_time(case_num, duration, file_writer)

                if case_num + 1 != len(num_list):
                    log_newline(file_writer)

        clear_screen()

        # Start of testing for primeLister()
        with open("./primeLister_testcase","w") as file_writer:
            
            for case_num, i in enumerate(num_list):
                sub_time_start = measure_time()

                case_desc = f"Listing all prime numbers till {i}:n"
                result = "".join([f" > {prime}n" for prime in primeLister(i)])

                log_testcase(case_num, case_desc, result, file_writer)

                duration = measure_time() - sub_time_start
                log_time(case_num, duration, file_writer)

                if case_num + 1 != len(num_list):
                    log_newline(file_writer)    

        clear_screen()

        # Start of testing for Twin_Primes()
        with open("./Twin_Primes_testcase","w") as file_writer:
            for case_num in range(len(num_list) - 1):
                sub_time_start = measure_time()

                number1, number2 = num_list[case_num], num_list[case_num + 1]
                case_desc = f"Listing all Twin Prime number pairs between {number1} and {number2}:n"
                result = "".join([f" > {twin}n" for twin in Twin_Primes(number1, number2)])
                
                log_testcase(case_num, case_desc, result, file_writer)

                duration = measure_time() - sub_time_start
                log_time(case_num, duration, file_writer)

                if case_num + 2 != len(num_list):
                    log_newline(file_writer)
                
                clear_screen()
        main_end_time = measure_time()
        print(f"Time taken for the testcase as a whole: {main_end_time-main_start_time:.3f} seconds")
        pass

t = threading.Thread(target=long_running_task)
t.start()

The testcase is also saved in the same folder locally.
The program stops abruptly during the execution of primeLister testcase after writing the primes up to 99991 in the file.

I guess that it stops during the process of listing primes between 99991 and 999999937. I’ve got no idea why.
My computer has an Intel i5-12450H processor with 16GB RAM. If that’s relevant.

I have already tried implementing an infinite loop, threading and also using exception handling. Nothing has worked so far. What am I doing wrong?

I was expecting the program to keep executing until it found all the primes within the provided range.