Generator function for prime numbers

Question

I am trying to write a generator function for printing prime numbers as follows

 def getPrimes(n):
    prime=True
    i=2
    while(i<n):
        for a in range(2,i):
            if(i%a==0):
                prime=False
                break
        if(prime):    
            yield i

However, I do not get the desired results. P = getPrimes (100) should give me a generator function that will iterate primes from 2 to 100, but the result that I get is [2,3]. What am I doing wrong?

Answer 1

You need to reset primeto Trueas the first statement inside the while block, and not before it. As soon as you click on one compound number, it primewill never be true again, so you will never get more numbers.

Answer 2

:

:

Prime Generator Python - .

2, 3, 5, 7 11. - .

def genprimes(limit): # derived from 
                      # Code by David Eppstein, UC Irvine, 28 Feb 2002
    D = {}            # http://code.activestate.com/recipes/117119/
    q = 2

    while q <= limit:
        if q not in D:
            yield q
            D[q * q] = [q]
        else:
            for p in D[q]:
                D.setdefault(p + q, []).append(p)
            del D[q]
        q += 1

p = genprimes(100)
prms = [i for i in p]

print prms

:

[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

Answer 3

, . :

def getPrimes(n):
    i = 2
    while i < n :
        prime = True # reset the `prime` variable before the inner loop
        for a in xrange(2, i):
            if i%a == 0:
                prime = False
                break
        if prime:    
            yield i
        i += 1 # don't forget to advance `i`

, , , , n:

def getPrimes(n):
    if n <= 2:
        raise StopIteration
    yield 2
    for i in xrange(3, n, 2):
        for x in xrange(3, int(i**0.5)+2, 2):
            if not i % x:
                break
        else:
            yield i

, :

[x for x in getPrimes(20)]
=> [2, 3, 5, 7, 11, 13, 17, 19]

Answer 4

def isprime(n):
    for i in range(2 ,int((n**0.5))+1):
        if n % i == 0:
            return False
    return True

def getPrimes(n):
    yield 2
    i = 1
    while i <= n-2:
        i += 2
        if isprime(i):
            yield i

Answer 5

, , reset prime. , , , .

, , , break, else :

def getPrimes(n):
    i = 2
    while i < n :
        for a in range(2, i):
            if i % a == 0:
                break
        else:    
            yield i

else , , break.

, , , i. ( - , , n ):

def getPrimes(n):
    yield 2
    i = 3
    while i < n:
        for a in getPrimes(int(math.sqrt(i))+1):
            if i % a == 0:
                break
        else:
            yield i
        i += 2