code: def get_completion_class(
      shell: str,
  ) -> t.Optional[t.Type[ShellComplete]]:
      """Look up a registered :class:`ShellComplete` subclass by the name
      provided by the completion instruction environment variable. If the
      name isn't registered, returns ``None``.
  
      :param shell: Name the class is registered under.
      """
      return _available_shells.get(shell)
  
imports: import os
  import re
  import typing
  from gettext import gettext
  from .core import Argument
  from .core import BaseCommand
  from .core import Context
  from .core import MultiCommand
  from .core import Option
  from .core import Parameter
  from .core import ParameterSource
  from .parser import split_arg_string
  from .utils import echo
label_desc: Use image node_id 3 for calling a global function with example usage: get_completion_class(shell) and returns: _available_shells