Can I pause itertools on python, and resume later?

Question

I need to create a list of strings with all the possible combinations of all letters uppercase and lowercase, with non repeating characters, of lenght 14, this is massive and I know it will take a lot of time and space. My code right now is this:

import itertools

filename = open("strings.txt", "w")

for com in itertools.permutations('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ', 14):
    filename.write("\n"+"1_"+"".join(com)+"\n"+"0_"+"".join(com))
    print ("".join(com))

pretty basic, it does the job and I have not found a faster way as of yet (tried a java algorithm I found that seemed faster but python was faster) Since this will take a long time, from time to time I need to turn off my computer, so I need to be able to save somewhere where I left and continue, else I will start from the beginning each time it crashes/turn off my pc / anything happen. Is there any way to do that?

Answer 1

You can pickle that iterator object. Its internal state will be stored in the pickle file. When you resume it should start from where it left off.

Something like this:

import itertools
import os
import pickle
import time

# if the iterator was saved, load it
if os.path.exists('saved_iter.pkl'):
    with open('saved_iter.pkl', 'rb') as f:
        iterator = pickle.load(f)
# otherwise recreate it
else:
    iterator = itertools.permutations('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ', 14)

try:
    for com in iterator:
        # process the object from the iterator
        print(com)
        time.sleep(1.0)
except KeyboardInterrupt:
    # if the script is about to exit, save the iterator state
    with open('saved_iter.pkl', 'wb') as f:
        pickle.dump(iterator, f)

Which results in:

>python so_test.py
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'o')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'p')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'q')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'r')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 's')

>python so_test.py
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 't')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'u')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'v')
('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'w')