查找素数和非素数：Python

Question

I am trying to modify my program to create two empty lists: prime and non_prime. and test if the random number in the list is a prime number or not a prime number. If the number is prime, I want to append it to prime number list. If not, I want to be able to add it to non_prime list. I tried to find the prime and non prime number from the random number list but I get the same output for prime and non prime number. Can anyone help me?

 import random

 def main():
      num = [random.randint(1,100) for _ in range (20)]
      print(num)

      lowest = min(num)
      print("The lowest number is: ", lowest)

      highest = max(num)
      print("The highest number is: ", highest)

     total = 0.0
     for value in num:
        total += value

     average = total / len(num)
     print("The average is: " , average)


     prime = [num]
     for a in range (1, 101):
        for b in range(2, a):
            if a % b == 0:
                break
        else:
            prime.append(a)
     print("The prime numbers are: " , prime)

    nonprime = [num]
    for x in range (1, 101):
        for y in range(2, x):
            if x % y == 0:
                break
        else:
            nonprime.append(x)
    print("The non prime numbers are: " , nonprime)

Answer 1

You could use my handy-dandy one-liner prime-checker!

def is_prime (x): return True if x in [2,3] else not any (x % n == 0 for n in range (2, int (x ** 0.5) + 1))

Now, you use this function in your for loop:

for num in range (1, 101): 
    if is_prime (num): prime.append (x)
    else: nonprime.append (x)

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BTW, if anyone wants to help me improve that function (or just wants to understand it), just comment below! It pretty much makes a list of all the factors then returns true or false based on the length of that list (or True if the num is 2 or 3)

Answer 2

Just an optimization tip. In the first loop you could calculate non prime and prime both.

def isPrime(x):
    for i in range (sqrt (x)): # from i=2 till sqrt(x)
        if x % i == 0: return False
    return True

if isPrime (x): prime.append (x)
else: non_prime.append (x)

The above is sieve algorithm