Increasing Primes

import operator

def prime_list(n):
    sieve = [True] * n
    for i in xrange(3, int(n ** 0.5) + 1, 2):
        if sieve[i]:
            sieve[i * i::2 * i]=[False]*((n - i * i - 1) / (2 * i) + 1)
    return [2] + [i for i in xrange(3, n, 2) if sieve[i]]

biggest_prime = 982451653
list_of_primes = prime_list(biggest_prime)

print('49,999,999 prime numbers generated...\n')

#-----------------------------------------------------------------------

last = 1

data = {}

for i, prime in enumerate(list_of_primes):
    num = i + 1
    percent_increase = ((prime / last) - 1) * 100

    data.update({prime : percent_increase})

    last = float(prime)

new = []

sorted_x = sorted(data.items(), key=operator.itemgetter(1))

for a, b in sorted_x:
    new.append(str(a) + ', (' + str(b) + '%)')

new = new[::-1] # Reverse list

with open('/path/to/results', 'w') as the_file:
    for item in new[:1000000]:
        the_file.write(str(item) + '\n')