Using alembic.config.main redirects log output

In case anyone comes across this issue here is what worked for me:

• Updating the fileConfig call in env.py: fileConfig(config.config_file_name, disable_existing_loggers = False)

• Updating the level for [logger_root] in alembic.ini to a lower level, since it is set by default to WARN

I just learned that fileConfig takes a keyword argument, disable_existing_loggers, which defaults to True. Simply adding disable_existing_loggers = False to the call to fileConfig in env.py e.g:

fileConfig(config.config_file_name, disable_existing_loggers=False)

appears to allow both logging configurations to work without interfering with each other (which may be preferred rather than having to choose one over the other, in some cases)

This is because alembic sets up logging using fileConfig from alembic.ini, you can see it in your env.py script:

# Interpret the config file for Python logging.
# This line sets up loggers basically.
fileConfig(config.config_file_name)

This effectively overrides your original logger config.

To avoid this, you can simply remove this line from env.py, however this will result in no logs being produced when running alembic from console.

A more robust option is to run alembic commands via alembic.command instead of alembic.config.main. This way you can override alembic config at runtime:

from alembic.config import Config
import alembic.command

config = Config('alembic.ini')
config.attributes['configure_logger'] = False

alembic.command.upgrade(config, 'head')

Then in env.py:

if config.attributes.get('configure_logger', True):
    fileConfig(config.config_file_name)