file_exists.py

from os import path

def isPrime(n):
    for d in range(2, n):
        if (n/ d).is_integer(): return False
    return True

#for i in range(100):
#    if isPrime(i): print(i)
    
def makePrimes(numToMake):
    primesFound = 0
    
    if path.exists('primes.txt'):
        with open('primes.txt', 'r') as f:
            lines = f.readlines()
            if len(lines) > 0:
                lastLine = lines[-1]
                val = int(lastLine)
            else: val = 2
            
    else: val = 2
    
    while primesFound < numToMake:
        with open('primes.txt', "a+") as f:
            if isPrime(val):
                f.write("\n"+str(val))
                primesFound += 1
            val += 1

makePrimes(10)