class_docstr: Singleton metaclass interface for
  :class:`fiftyone.core.document.Document` subclasses.
  
  The methods declared by this interface are used by the
  :class:`fiftyone.core.document.Document` class to manage all instances
  of a class that implements this type.
docstr: Reloads the backing document for the given instance (or view), if a
  reference exists to it.
  
  Args:
      obj: a :class:`Document` or :class:`DocumentView`
docstr_tok: ["Reloads","the","backing","document","for","the","given","instance","(","or","view",")",",","if","a","reference","exists","to","it",".","Args",":","obj",":","a",":","class",":","`","Document","`","or",":","class",":","`","DocumentView","`"]
code: def _reload_instance(cls, obj):
      """Reloads the backing document for the given instance (or view), if a
      reference exists to it.
  
      Args:
          obj: a :class:`Document` or :class:`DocumentView`
      """
      raise NotImplementedError(
          "subclass must implement _reload_instance()"
      )
  
imports: from collections import defaultdict
  import weakref
label_desc: Use image node_id 3 for calling the DocumentSingleton obj's underlying member method code with example usage: obj._reload_instance(cls, obj) without return types