Question

I’ve searched, but found nothing to help.. This is an example:

    List.txt
    a
    b
    c
    d

I want to be able to get an output like this:

    Output.txt
    ab
    ac
    ad
    ba
    bc
    bd
    ca
    cb
    cd
    etc...

Answer 1

Pretty straightforward…

from itertools import permutations

with open('List.txt') as f:    
    letters = (l.strip() for l in f if l.strip())    
    for p in permutations(letters, 2):
        print ''.join(p)

Output:

ab
ac
ad
ba
bc
bd
ca
cb
cd
da
db
dc

Some notes:

The with statement ensures the file will be closed when you’re done with it.

letters is a generator expression, which in many cases (though not this one) will save you from having to read the entire file in at once.

The uses of l.strip() are meant to nicely handle accidental blank lines if present in input.

itertools.permutations is correct, NOT itertools.combinations which considers ab == ba and will not include the latter as output.

Happy pythoning 🙂