Untested but something like this:

from sqlalchemy import inspect
old_to_new = {c.name: k for k, c in inspect(TableName).columns.items()}

https://docs.sqlalchemy.org/en/20/orm/mapping_api.html#sqlalchemy.orm.Mapper.columns

https://docs.sqlalchemy.org/en/20/orm/mapping_styles.html#inspection-of-mapper-objects