dan's efficient primes | Python Fiddle

def findPrimesInRange (startnum, finishnum):
    """
    This function finds all primes within a given positive integer range and returns them as a list
    """
    #Initialize
    
    primes = [i for i in range(startnum, finishnum) if all(i%j for j in range(2,i)) and i >= 2]
    
    return primes

#x, y = 60, 100
x, y = input('Enter range as positive integers x, y:\n')

if x > y:
    print('x > y:  Swapping endpoints\n')
    x, y = y, x
#primes = findPrimesInRange(x, y)
chunkstart = x
chunkend = y
increment = 10
primes = []
#I'd like to make this section a generic function for handling chunks sometime.
while chunkstart < chunkend:
    if chunkstart + increment > y:
        chunkend = y
        #print(chunkstart,chunkend)
        moreprimes = findPrimesInRange(chunkstart, chunkend)
        #print('Foundprimes {0}'.format(moreprimes))
    else:
        chunkend =chunkstart + increment
        #print(chunkstart,chunkend)
        moreprimes = findPrimesInRange(chunkstart, chunkend)
    	#print('Foundprimes {0}'.format(moreprimes))
    primes += moreprimes
    chunkstart = chunkend
    chunkend=y
    #print(chunkstart,chunkend)
    
#print(primes)

print('\nThere are {0} primes in range {1} - {2}\n'.format(len(primes),x,y))
for i in range(0,len(primes),increment):
    print(primes[i:i+increment])

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