如何在 Python 中获得每个 6 元素的重复排列？

Question

I want to create a list of all possible 6-element permutations from "abcdefghijklmnopqrstuvwxyz0123456789" so for example it should output:

['aaaaaa','aaaaab','aaaaac'...,'aaaaa0','aaaaa1'...,'aaaaba','aaaabb'...] and so on.

This is what I tried:

import itertools

dictionary = 'abcdefghijklmnopqrstuvwxyz0123456789'
print(list(itertools.product(dictionary, repeat=6)))

but I ran into a MemoryError and then my computer froze up completely, so is there a more efficient way to compute this list?

(I'm using Python 3.8 64-bit)

Answer 1

Do you know how long your list would be? It is 36**6 = 2176782336 items. A bit too much to hold in memory. You should have used a generator:

dictionary = 'abcdefghijklmnopqrstuvwxyz0123456789'
for x in itertools.product(dictionary, repeat=6):
    print(''.join(x))

Answer 2

The size of the permutation is huge: 36^6. That's 2176782336 strings. A 6-char string in python is already relatively large due to how python stores separate objects.

from sys import getsizeof

getsizeof('aaaaaa') # 55

At 55 bytes per string, the whole list is almost 120 Gigabytes. You probably don't much have memory on your machine.

If you try to convert this iterator to a list, it will generate all permutations at once. What you can do instead is to use the iterator returned by itertools.product(dictionary, repeat=6) without converting it to a list.

for s in itertools.product(dictionary, repeat=6):
    # Do something with the string, such as writing it to a file.

Without knowing what you are trying to do with the product, I can't specifically tell you how to optimize this. But I can still say that trying to convert this iterator to a list is a bad idea.