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!

[Gribouillis]

I'm clearly doing something wrong

Your generator is generating a single item which is the whole list of subdirectories.

You could return the whole generator

def scan_dir(dir):
    return (str(x) for x in dir.iterdir() if x.is_dir())

or

import os
def scan_dir(dir):
    for name in next(os.walk(dir))[1]:
        yield os.path.join(dir, name)

or

import os
def scan_dir(dir):
    return (x.path for x in os.scandir(dir) if x.is_dir())

I think the last one is better.

[tester_V]

So, it is not possible to use "yield" with the list comprehension. Right?
Thank you!

[Gribouillis]

So, it is not possible to use "yield" with the list comprehension.

Yes you could use yield from

def func():
    yield from range(3)
    yield from (x**2 for x in range(2, 7))

[snippsat]

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

It will not speed things,and the list comprehensions will create the list in memory unnecessary.
The point with yield is that it keep it it a lazy iterators do not store the whole content of data in the memory.
So then could write it like this.

from pathlib import Path

def scan_dir(some_dir):
    for sbd in some_dir.iterdir():
        if sbd.is_dir:
            yield sbd

if __name__ == '__main__':
    some_dir = Path('C:\\Python27')
    for i in scan_dir(some_dir):
        print(f" Subdirectories -> {i}")

Output:
Subdirectories -> C:\Python27\DLLs
Subdirectories -> C:\Python27\Doc
Subdirectories -> C:\Python27\include
.....

[tester_V]

Thank you!