class_docstr: An abstract class representing subcommands for allennlp.run.
  If you wanted to (for example) create your own custom `special-evaluate` command to use like
  
  `allennlp special-evaluate ...`
  
  you would create a `Subcommand` subclass and then pass it as an override to
  [`main`](#main).
code: def register(  # type: ignore
      cls: Type[T],
      name: str,
      constructor: Optional[str] = None,
      exist_ok: bool = False,
  ) -> Callable[[Type[T]], Type[T]]:
      super_register_fn = super().register(
          name, constructor=constructor, exist_ok=exist_ok
      )
  
      def add_name_to_reverse_registry(subclass: Type[T]) -> Type[T]:
          subclass = super_register_fn(subclass)
          # Don't need to check `exist_ok`, as it's done by super.
          # Also, don't need to delete previous entries if overridden, they can just stay there.
          cls._reverse_registry[subclass] = name
          return subclass
  
      return add_name_to_reverse_registry
  
imports: import argparse
  from typing import Callable, Dict, Optional, Type, TypeVar
  from allennlp.common import Registrable
label_desc: Use image node_id 2 for calling the Subcommand obj's underlying member method code with example usage: obj.register(cls, name, constructor, exist_ok) and returns: add_name_to_reverse_registry, subclass