Running pihole 5.1.2 in docker container.
/etc/pihole is /home/pi/IOTstack/volumes/pihole/etc-pihole/
python 3.7.3 is installed

The installation instructions are interpreted to use the following to install, based upon how this pihole is running, after performing a successful git clone.

sudo python3 whitelist/scripts/whitelist.py --dir /home/pi/IOTstack/volumes/pihole/etc-pihole/ --docker

The script starts.
Result is:

This script will download and add domains from the repo to whitelist.
All the domains in this list are safe to add and does not contain any tracking or adserving domains.

[i] Pi-hole path exists
[i] Write access to /home/pi/IOTstack/volumes/pihole/etc-pihole/ verified
Traceback (most recent call last):
File "whitelist/scripts/whitelist.py", line 141, in
if os.path.isfile(gravity_db_location) and os.path.getsize(gravity_db_location) > 0 and getPiholeVersion() >= 51:
File "whitelist/scripts/whitelist.py", line 61, in getPiholeVersion
pihole_version = subprocess.Popen(['pihole', 'version', '-p', '-c'], stdout=subprocess.PIPE)
File "/usr/lib/python3.7/subprocess.py", line 775, in init
restore_signals, start_new_session)
File "/usr/lib/python3.7/subprocess.py", line 1522, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'pihole': 'pihole'