Generating character permutations
Not much to do there, maybe use with ... as and inline everything:

from itertools import product

with open('myfile', 'w') as file:
    for p in product('ABCDEFGHIJKLMNOPQRSTUVWXYZ', repeat=8):
        file.write("".join(p) + "\n")


I'm sure there is a clever way to generate the characters as well. Edit: ah yes, you could replace 'A...Z' with map(chr, range(65, 91)) although
that seems rather cryptic.

Now why would you want that though? It seems that using that generator and
staying in Python would be more than enough instead of generating a static
file.