code: def get_fn_or_method(callable):
      
      if _inspect.isfunction(callable) or _inspect.ismethod(callable):
          return callable
      if _inspect.isclass(callable):
          return callable.__init__
      return callable.__call__
docs: Returns the underlying function or method that will be called by the () operator.
  
          * For regular functions and methods, returns ``callable``
          * For classes, returns ``callable.__init__``
          * For callable objects, returns ``callable.__call__``