code: def _str_index(self):
      idx = self["index"]
      out = []
      out += [".. index:: %s" % idx.get("default", "")]
      for section, references in idx.iteritems():
          if section == "default":
              continue
          out += ["   :%s: %s" % (section, ", ".join(references))]
      return out
  
imports: import inspect
  import textwrap
  import re
  import pydoc
  from warnings import warn
label_desc: Use image node_id 21 for calling the NumpyDocString obj's underlying member method code with example usage: obj._str_index() and returns: out