Per my understanding there should be either db_username+db_password or db_connect_file. But per @Vladis13 it seems like db_username is sometimes ignored even if no db_connect_file is given.

Probably not bug in the documentation, but in Pywikibot MySQL I think as the connect file shouldn't be used if username and password set

Not even driver-dependent.

db_connect_file = user_home_path('.my.cnf')

if config.db_connect_file is None:
    credentials = {'user': config.db_username,
                   'passwd': config.db_password}
else:
    credentials = {'read_default_file': config.db_connect_file}

As there is always db_connect_file set in config2 (if not explicitly set to None in user-config like @Vladis13 discovered), the if should be the other way around I think: if (not) db_username:

@Dvorapa the db_connect_file is also set in the user_config.py , Is the update of @zhuyifei1999 code been done in the user_config.py ?

I'll like to work on this task.

@Ngwebecky96: Hi and welcome! Please investigate, and try yourself. :) Also see https://www.mediawiki.org/wiki/New_Developers - thanks a lot!