Ban certain users by using ACCOUNT_USERNAME_BLACKLIST (=[]) and getting data from a .txt file
Yes. You can just read in the text file in your settings file.
Its a common practice done where people will often load in a json file that contains values for a load of different settings that may change depending on environment.
I am using Django and All-auth. I want to restrict users to take certain usernames. I know that it is done through writing the following in  settings.py.
ACCOUNT_USERNAME_BLACKLIST (=[])
But I want to take this list from a .txt file. Should I read the .txt file in my settings.py and then populate the ACCOUNT_USERNAME_BLACKLIST (=[]) list? Or there is some other way that is more reasonable and considered as a best practice?