code: def clear_mappers() -> None:
      """Remove all mappers from all classes.
  
      .. versionchanged:: 1.4  This function now locates all
         :class:`_orm.registry` objects and calls upon the
         :meth:`_orm.registry.dispose` method of each.
  
      This function removes all instrumentation from classes and disposes
      of their associated mappers.  Once called, the classes are unmapped
      and can be later re-mapped with new mappers.
  
      :func:`.clear_mappers` is *not* for normal use, as there is literally no
      valid usage for it outside of very specific testing scenarios. Normally,
      mappers are permanent structural components of user-defined classes, and
      are never discarded independently of their class.  If a mapped class
      itself is garbage collected, its mapper is automatically disposed of as
      well. As such, :func:`.clear_mappers` is only for usage in test suites
      that re-use the same classes with different mappings, which is itself an
      extremely rare use case - the only such use case is in fact SQLAlchemy's
      own test suite, and possibly the test suites of other ORM extension
      libraries which intend to test various combinations of mapper construction
      upon a fixed set of classes.
  
      """
  
      mapperlib._dispose_registries(mapperlib._all_registries(), False)
  
imports: from __future__ import annotations
  import typing
  from typing import Any
  from typing import Callable
  from typing import Collection
  from typing import Iterable
  from typing import NoReturn
  from typing import Optional
  from typing import overload
  from typing import Type
  from typing import TYPE_CHECKING
  from typing import Union
  from .None import mapperlib
  from ._typing import _O
  from .descriptor_props import Composite
  from .descriptor_props import Synonym
  from .interfaces import _AttributeOptions
  from .properties import MappedColumn
  from .properties import MappedSQLExpression
  from .query import AliasOption
  from .relationships import _RelationshipArgumentType
  from .relationships import _RelationshipSecondaryArgument
  from .relationships import Relationship
  from .relationships import RelationshipProperty
  from .session import Session
  from .util import _ORMJoin
  from .util import AliasedClass
  from .util import AliasedInsp
  from .util import LoaderCriteriaOption
  from ..None import sql
  from ..None import util
  from ..exc import InvalidRequestError
  from ..sql._typing import _no_kw
  from ..sql.base import _NoArg
  from ..sql.base import SchemaEventTarget
  from ..sql.schema import _InsertSentinelColumnDefault
  from ..sql.schema import SchemaConst
  from ..sql.selectable import FromClause
  from ..util.typing import Annotated
  from ..util.typing import Literal
label_desc: Use image node_id 18 for calling a global function with example usage: clear_mappers() without return types