code: def _auto_fn(name: str) -> Optional[Callable[[], Type[Dialect]]]:
      """default dialect importer.
  
      plugs into the :class:`.PluginLoader`
      as a first-hit system.
  
      """
      if "." in name:
          dialect, driver = name.split(".")
      else:
          dialect = name
          driver = "base"
  
      try:
          if dialect == "mariadb":
              # it's "OK" for us to hardcode here since _auto_fn is already
              # hardcoded.   if mysql / mariadb etc were third party dialects
              # they would just publish all the entrypoints, which would actually
              # look much nicer.
              module = __import__(
                  "sqlalchemy.dialects.mysql.mariadb"
              ).dialects.mysql.mariadb
              return module.loader(driver)  # type: ignore
          else:
              module = __import__(
                  "sqlalchemy.dialects.%s" % (dialect,)
              ).dialects
              module = getattr(module, dialect)
      except ImportError:
          return None
  
      if hasattr(module, driver):
          module = getattr(module, driver)
          return lambda: module.dialect
      else:
          return None
  
imports: from __future__ import annotations
  from typing import Callable
  from typing import Optional
  from typing import Type
  from typing import TYPE_CHECKING
  from ..None import util
label_desc: Use image node_id 1 for calling a global function with example usage: _auto_fn(name) and returns: function, None, module, None