Python - Brute Force - Memory Error

Question

I am working on this code that generates sequences with all the possibilities of the characters entered(your_list)

your_list = 'abcdefghijklmnopqrstuvwxyz'
complete_list = []
for current in range(10):
    a = [i for i in your_list]
    for y in range(current):
         a = [x+i for i in your_list for x in a]
    complete_list = complete_list+a
print (complete_list)

I’m finding the error highlighted below, but I don’t know how to solve this problem

"C:\Users\admin\PycharmProjects\markestrat\venv\Scripts\python.exe" "C:/Users/admin/PycharmProjects/markestrat/venv/brutef.py"
Traceback (most recent call last):
  File "C:/Users/admin/PycharmProjects/markestrat/venv/brutef.py", line 65, in <module>
    a = [x+i for i in your_list for x in a]
  File "C:/Users/admin/PycharmProjects/markestrat/venv/brutef.py", line 65, in <listcomp>
    a = [x+i for i in your_list for x in a]
MemoryError

Does anyone know how to solve this problem?

Answer 1

You can get the lowercase letters of the alphabet with:

from string import ascii_lowercase

If you want all letters, including uppercase, string.ascii_letters, or only capital letters, string.ascii_uppercase, or any available value in string.

To generate all possible combinations of N characters, without repetition, keeping the order of the same, you can use itertools.combinations:

from itertools import combinations
from string import ascii_lowercase

print(list(combinations(ascii_lowercase, 2)))

The return of this would be

[('a', 'b'), ('a', 'c'), ('a', 'd'), ..., ('x', 'y'), ('x', 'z'), ('y', 'z')]

Thus, you could define a function that generates all possible combinations without doing repetition:

def all_combinations(iterable):
    size = len(iterable)
    for i in range(1, size+1):
        yield from combinations(iterable, i)

This will generate all possible combinations of 1 to 26 characters, without repetition and maintaining order, but without storing all the values in memory. How generators are used, each value is generated on demand, implementing what we call Lazy-Evaluation and thus circumventing the memory problem presented in the question.

Notes

1. The return is an eternal object of tuples with the combination; if it is desirable a string, such conversion should be treated;
2. All combinations respect the order of the input characters, so the combination is generated ('a', 'b') but not the ('b', 'a');
3. All combinations are without repetition, not generating sequences with the same character as for example ('a', 'a', 'a'); if desired with repetition, use itertools.combinations_with_replacement;