My prime number finding code is trying all numbers so it will print the prime number a few times. Eg: 5/2 , 5/3, 5/4. So it will print 5 for 3 times.

def prime_number_generator(num):
    for n in range (1,num):
        for prime in range (2,n):
            if (n%prime) ==0:
                break
            else:
                yield n

number = input('Please input the number:') 
if number.isnumeric():
    num = int(number)
    if num <= 2:
        print('Number must be greater than 2') 
    else: 
        for prime in prime_number_generator(num):
            print(prime, end=', ') 
else: 
    print('Must be a positive integer') 

Output with input as 27:

3, 5, 5, 5, 7, 7, 7, 7, 7, 9, 11, 11, 11, 11, 11, 11,
 11, 11, 11, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 
15, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 
17, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 
19, 19, 21, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 
23, 23, 23, 23, 23, 23, 23, 23, 25, 25, 25,

CodePudding user response：

That's not your only problem. You are also (incorrectly) returning 15 as prime because you are immediately assuming that the number is prime if it can't be divided by 2 (the first iteration of your second for loop). Try this (note the indentation of the else):

def prime_number_generator(num):
    for n in range (2, num):
        for prime in range (2, n):
            if (n % prime) == 0:
                break
        else:
            yield n

See this question for an explanation of for..else construct in Python.

CodePudding user response：

The Problem

In this function:

def prime_number_generator(num):
    for n in range (1,num):
        for prime in range (2,n):
            if (n%prime) ==0:
                break
            else:
                yield n

You are yielding n if it is not exactly divisible by prime. Here is an example for what happens when n = 5:

• First, prime = 2. n % prime != 0, so n, i.e, 5 is yielded
• Then, prime = 3. n % prime != 0, so 5 is, once again, yielded
• Then, prime = 4, n % prime != 0, so 5 is, once again, yielded
• Finally, prime = 5. n % prime == 0, so the loop is broken.

This process is then repeated with the next n

How to fix

You can remove the else clause from the if, and add it to the for loop. This means that n will be yielded only if the for loop was not broken, that is, only if n is not divisible by any number between 2 and n - 1.

So you can rewrite your function like this:

def prime_number_generator(num):
    for n in range (1, num):
        for prime in range (2, n):
            if (n % prime) == 0:
                break
        else:
            yield n

CodePudding user response：

def is_prime(n):
    for i in range(2, n):
        if n % i == 0:
            return False
        else:
            return True
        
def get_prime_numbers(n):
    for i in range(2, n):
        if is_prime(i):
            yield i
            
prime_numers = [prime for prime in get_prime_numbers(20)]
print(prime_numers)