There's a lot of confusion on this topic. Let me see if I can clarify it (Python 3.7):

1. glob.glob('*.txt') :matches all files ending in '.txt' in current directory
2. glob.glob('*/*.txt') :same as 1
3. glob.glob('**/*.txt') :matches all files ending in '.txt' in the immediate subdirectories only, but not in the current directory
4. glob.glob('*.txt',recursive=True) :same as 1
5. glob.glob('*/*.txt',recursive=True) :same as 3
6. glob.glob('**/*.txt',recursive=True):matches all files ending in '.txt' in the current directory and in all subdirectories

So it's best to always specify recursive=True.

files = glob.glob('/ParentDirectory/*/*.csv')

It doesn't need to be recursive for that pattern, but does need a wildcard for the subdirectory.

Much nicer than the above, because you don't need several os.path.join() and you will get the full path directly (if you wish), you can do this in Python 3.5 and above.

subfolders = [ f.path for f in os.scandir(folder) if f.is_dir() ]

This will give the complete path to the subdirectory. If you only want the name of the subdirectory use f.name instead of f.path

https://docs.python.org/3/library/os.html#os.scandir

Slightly OT: In case you need all subfolder recursively and/or all files recursively, have a look at this function, that is faster than os.walk & glob and will return a list of all subfolders as well as all files inside those (sub-)subfolders: https://stackoverflow.com/a/59803793/2441026

In case you want only all subfolders recursively:

def fast_scandir(dirname):
    subfolders= [f.path for f in os.scandir(dirname) if f.is_dir()]
    for dirname in list(subfolders):
        subfolders.extend(fast_scandir(dirname))
    return subfolders

Returns a list of all subfolders with their full paths. This again is faster than os.walk and a lot faster than glob.

An analysis of all functions

tl;dr:
- If you want to get all immediate subdirectories for a folder use os.scandir.
- If you want to get all subdirectories, even nested ones, use os.walk or - slightly faster - the fast_scandir function above.
- Never use os.walk for only top-level subdirectories, as it can be hundreds(!) of times slower than os.scandir.

• If you run the code below, make sure to run it once so that your OS will have accessed the folder, discard the results and run the test, otherwise results will be screwed.
• You might want to mix up the function calls, but I tested it, and it did not really matter.
• All examples will give the full path to the folder. The pathlib example as a (Windows)Path object.
• The first element of os.walk will be the base folder. So you will not get only subdirectories. You can use fu.pop(0) to remove it.
• None of the results will use natural sorting. This means results will be sorted like this: 1, 10, 2. To get natural sorting (1, 2, 10), please have a look at https://stackoverflow.com/a/48030307/2441026

Results:

os.scandir      took   1 ms. Found dirs: 439
os.walk         took 463 ms. Found dirs: 441 -> it found the nested one + base folder.
glob.glob       took  20 ms. Found dirs: 439
pathlib.iterdir took  18 ms. Found dirs: 439
os.listdir      took  18 ms. Found dirs: 439

Tested with W7x64, Python 3.8.1.

# -*- coding: utf-8 -*-
# Python 3


import time
import os
from glob import glob
from pathlib import Path


directory = r"<insert_folder>"
RUNS = 1


def run_os_walk():
    a = time.time_ns()
    for i in range(RUNS):
        fu = [x[0] for x in os.walk(directory)]
    print(f"os.walk\t\t\ttook {(time.time_ns() - a) / 1000 / 1000 / RUNS:.0f} ms. Found dirs: {len(fu)}")


def run_glob():
    a = time.time_ns()
    for i in range(RUNS):
        fu = glob(directory + "/*/")
    print(f"glob.glob\t\ttook {(time.time_ns() - a) / 1000 / 1000 / RUNS:.0f} ms. Found dirs: {len(fu)}")


def run_pathlib_iterdir():
    a = time.time_ns()
    for i in range(RUNS):
        dirname = Path(directory)
        fu = [f for f in dirname.iterdir() if f.is_dir()]
    print(f"pathlib.iterdir\ttook {(time.time_ns() - a) / 1000 / 1000 / RUNS:.0f} ms. Found dirs: {len(fu)}")


def run_os_listdir():
    a = time.time_ns()
    for i in range(RUNS):
        dirname = Path(directory)
        fu = [os.path.join(directory, o) for o in os.listdir(directory) if os.path.isdir(os.path.join(directory, o))]
    print(f"os.listdir\t\ttook {(time.time_ns() - a) / 1000 / 1000 / RUNS:.0f} ms. Found dirs: {len(fu)}")


def run_os_scandir():
    a = time.time_ns()
    for i in range(RUNS):
        fu = [f.path for f in os.scandir(directory) if f.is_dir()]
    print(f"os.scandir\t\ttook {(time.time_ns() - a) / 1000 / 1000 / RUNS:.0f} ms.\tFound dirs: {len(fu)}")


if __name__ == '__main__':
    run_os_scandir()
    run_os_walk()
    run_glob()
    run_pathlib_iterdir()
    run_os_listdir()

Use the recursive argument to control how deep glob goes down. If you set recursive=False it will only match files in the current directory

Looks like this:

logs = glob('/var/opt/server/log/current/*', recursive=False)

For python >= 3.5 you can use **, recursive=True, i.e.:

import glob
for f in glob.glob('/path/**/*.c', recursive=True):
    print(f)

If recursive is True (default False), the pattern ** will match any files and zero or more directories and subdirectories. If the pattern is followed by an os.sep, only directories and subdirectories match.

Python 3 Demo