# How to use 'simple prime number program in python' in Python

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``20def prime(num):21    # num is actually a string because input() returns strings. We'll convert it to int22    num = int(num)2324    if num < 0:25        print("Negative integers can not be prime")26        quit()27    if num is 1:28        print("1 is neither prime nor composite")29        # See how I lazily terminated program otherwise it'd forward "None"(default behaviour of python when function30        # returns nothing) rather than True or False. Which could mess up the program.31        # If we hit this if statement above statement is printed then program exits.32        quit()  # Now you don't need to get sys.exit() to exit python has quit to handle the same thing33    if num in [2, 3]:34        # if given argument is 2 or 3, it is prime. We used list without defining a variable which is perfectly valid35        return True36    if num % 2 == 0:  # excluding all even numbers except two.37        return False38    else:39        # Here we are starting counter variable from 3 in range. Second argument excludes numbers above one third40        # of the given argument. Third argument in range sets steps to take to 2. This makes loop to iterate odds41        for x in range(3, int(num/3), 2):42            # Checking if argument is divisible by counter. % is modulus operator which returns remainder of division43            if num % x == 0:44                return False45    # It's okay to have more than one return statement when program hits return statement it exits the function.46    return True``
``746def prime_number_factorisation(n):747    if n < 2:748        return [n]749    i = 2750    factors = []751    while i * i <= n:752        if n % i:753            i += 1754        else:755            n //= i756            factors.append(i)757    if n > 1:758        factors.append(n)759    return factors``