def _auto_fn(name):
    if "." in name:
        dialect, driver = name.split(".")
    else:
        dialect = name
        driver = "base"
    try:
        module = __import__('sqlalchemy.dialects.%s' % (dialect, )).dialects
    except ImportError:
        return None

    module = getattr(module, dialect)
    if hasattr(module, driver):
        module = getattr(module, driver)
        return lambda: module.dialect
    else:
        return None
default dialect importer.
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/sqlalchemy/dialects/__init__.py/_auto_fn