Permutations of n elements into r groups Python

I don’t know how to create an algorithm / which to use for the following problem:

If I have a set of 20 elements (e.g. A -> T) and have a string of length 8, what are the permutations I could make? (I know there’s around 390 million)

e.g. we could have ABCDEFGH or EFHGATRI.

Does anyone have any ideas to help me?

>Solution :

Python has specific function for your issue itertools.permutations

Return successive r length permutations of elements in the iterable.

So, you can use it for your task

["".join(x) for x in itertools.permutations("abcd", 3)]

> ['abc', 'abd', 'acb', 'acd', 'adb', 'adc', 'bac', 'bad', 'bca', 'bcd', 'bda', 'bdc', 'cab', 'cad', 'cba', 'cbd', 'cda', 'cdb', 'dab', 'dac', 'dba', 'dbc', 'dca', 'dcb']

Also, you can use generators to reduce RAM usage

def perms():
    for perm in itertools.permutations("abcdefghij", 5):
        yield "".join(perm)

for p in perms():
    print(p)