On Python ≥ 3.5, use 'pathlib.Path.mkdir':
For older versions of Python, Try os.path.exists, and consider os.makedirs for the creation:
import os
# checking if the directory demo_folder
# exist or not.
if not os.path.exists("path/to/demo_folder"):
# if the demo_folder directory is not present
# then create it.
os.makedirs("path/to/demo_folder")