class_docstr: MetadataCatalog is a global dictionary that provides access to
  :class:`Metadata` of a given dataset.
  
  The metadata associated with a certain name is a singleton: once created, the
  metadata will stay alive and will be returned by future calls to ``get(name)``.
  
  It's like global variables, so don't abuse it.
  It's meant for storing knowledge that's constant and shared across the execution
  of the program, e.g.: the class names in COCO.
class_docstr_tok: ["MetadataCatalog","is","a","global","dictionary","that","provides","access","to",":","class",":","`","Metadata","`","of","a","given","dataset",".","The","metadata","associated","with","a","certain","name","is","a","singleton",":","once","created",",","the","metadata","will","stay","alive","and","will","be","returned","by","future","calls","to","``","get","(","name",")","``",".","It","'s","like","global","variables",",","so","do","n't","abuse","it",".","It","'s","meant","for","storing","knowledge","that","'s","constant","and","shared","across","the","execution","of","the","program",",","e.g",".",":","the","class","names","in","COCO","."]
code: def __str__(self):
      return "MetadataCatalog(registered metadata: {})".format(
          ", ".join(self.keys())
      )
  
imports: import copy
  import logging
  import types
  from collections import UserDict
  from typing import List
  from detectron2.utils.logger import log_first_n
label_desc: Use image node_id 4 for calling the _MetadataCatalog obj's underlying member method code with example usage: obj.__str__() and returns: str