Using list comprehension with 'yield' in function

[tester_V]

Greetings!
I'm trying to speed up my script and I thought I'll use List Comprehensions in a Function.

 from pathlib import Path
some_dir = 'C:\\Python27'

def scan_dir(some_dir) :
    dirs = [str(sbd) for sbd in Path(some_dir).iterdir() if sbd.is_dir()]
    yield dirs

sub_dirs=scan_dir(some_dir)
for i in sub_dirs :
    print(f" Subdirectories -> {i}") 

I was expecting and output like this:

                   Subdirectories -> C:\Python27\DLLs
                   Subdirectories -> C:\Python27\Doc
                   Subdirectories -> C:\Python27\include
                   Subdirectories -> C:\Python27\Lib
                   Subdirectories -> C:\Python27\libs
                   Subdirectories -> C:\Python27\Scripts
                   Subdirectories -> C:\Python27\tcl
                   Subdirectories -> C:\Python27\Tools

Instead I got this:

                   Subdirectories -> ['C:\\Python27\\DLLs', 'C:\\Python27\\Doc', 'C:\\Python27\\include', 'C:\\Python27\\Lib', 'C:\\Python27\\libs', 'C:\\Python27\\Scripts', 'C:\\Python27\\tcl', 'C:\\Python27\\Tools']

I'm clearly doing something wrong, I just do not see what it is...
Thank you in advance!