Question

I am writing a program which contains a function that checks if a number is prime— if it is, it adds it to a specific list, then uses the pickle module to save it as a file. When the function is called again, it opens the list (using pickle), then checks if the number is in the list. If it is, it is a prime, if not, it checks if it is a prime using a pretty basic technique.

Here is my code:

'''
List of functions:
_isPrime(n)_ : checks if n is a prime number
_remove(n)_ : removes n from the running list of primes and updates the pkl file
_prevPrimes(n)_ : generates a list of primes up to n
_view()_ : imports and prints pList
_delete()_ : deletes all of pList
'''
def isPrime(n):
    import pickle
    from math import sqrt
    pList = pickle.load(open('primes.pkl', 'rb'))
    x=2
    if (type(n) != int) and (type(n) != long):
        print "N is not an integer."
        return False
    if n in pList:
       print "%d is a prime number." % (n)
       return True
    else:
        while (sqrt(n) >= x):
            if ((n%x) != 0):
               x = x + 1
               if (sqrt(n) < x):
                   pList.append(n)
                   pList = sorted(pList)
                   pickle.dump(pList, open('primes.pkl', 'wb'))
                   print "%d is a prime number." % (n)
                   return True
            if ((n%x)==0):
                print "%d is not a prime number." % (n)
                return False
    pList = sorted(pList)
    pickle.dump(pList, open('primes.pkl', 'wb'))

# NEW FUNCTION

def prevPrimes(n):
    from time import clock
    startTime= clock()
    import pickle
    from math import sqrt
    pList = pickle.load(open('primes.pkl', 'rb'))
    z = abs((max(pList)) - n)
    y= max(pList)
    if (z==0):
        print "Done"
    while (y <= n):
        pList = pickle.load(open('primes.pkl', 'rb'))
        if isPrime(y):
           if y not in pList:
               pList.append(y)
        y= y + 1
        pList = sorted(pList)
        pickle.dump(pList, open('primes.pkl', 'wb'))
    print startTime

# NEW FUNCTION

def remove(n):
    import pickle
    pList = pickle.load(open('primes.pkl', 'rb'))
    view()
    pList.remove(n)
    pickle.dump(pList, open('primes.pkl', 'wb'))
    view()

# NEW FUNCTION

def view():
    import pickle
    pList = pickle.load(open('primes.pkl', 'rb'))
    print pList

# NEW FUNCTION

def delete():
    import pickle
    pList = [2, 3, 5]
    pickle.dump(pList, open('primes.pkl', 'wb'))
    view()

It works fine in the Python shell.

The error that occurs is if the function actually calls. I accomplished this by doing from primenum import isPrime. However, then it gets an error with the I/O (with pickle)… Here’s a picture:

As you can see, the primes.pkl file is clearly there.

How do I fix this? Thanks in advance for any suggestions 🙂

Answer 1

You already discovered how to import your function correctly:

from primenum import isPrime

or refer to the full name:

import primenum
primenum.isPrime(5)

You need to use a full path to store your pickle file; otherwise python looks for it in the local directory only. Perhaps store it in your home directory:

import os.path

HOME_DIR = os.path.expanduser('~')

then later open the file with:

open(os.path.join(HOME_DIR, 'primes.pkl')