docs: def parse_nestings2(string, nesters=['()', '[]', '<>', "''", '""'], escape='\\'):
      r"""
      References:
          http://stackoverflow.com/questions/4801403/pyparsing-nested-mutiple-opener-clo
  
      Example:
          >>> # DISABLE_DOCTEST
          >>> from utool.util_gridsearch import *  # NOQA
          >>> import utool as ut
          >>> string = r'lambda u: sign(u) * abs(u)**3.0 * greater(u, 0)'
          >>> parsed_blocks = parse_nestings2(string)
          >>> print('parsed_blocks = {!r}'.format(parsed_blocks))
          >>> string = r'lambda u: sign("\"u(\'fdfds\')") * abs(u)**3.0 * greater(u, 0)'
          >>> parsed_blocks = parse_nestings2(string)
          >>> print('parsed_blocks = {!r}'.format(parsed_blocks))
          >>> recombined = recombine_nestings(parsed_blocks)
          >>> print('PARSED_BLOCKS = ' + ut.repr3(parsed_blocks, nl=1))
          >>> print('recombined = %r' % (recombined,))
          >>> print('orig       = %r' % (string,))
      """
      import utool as ut  # NOQA
      import pyparsing as pp
  
      def as_tagged(parent, doctag=None):
          """Returns the parse results as XML. Tags are created for tokens and lists that have defined results names."""
          namedItems = dict((v[1], k) for (k, vlist) in parent._ParseResults__tokdict.items()
                            for v in vlist)
          # collapse out indents if formatting is not desired
          parentTag = None
          if doctag is not None:
              parentTag = doctag
          else:
              if parent._ParseResults__name:
                  parentTag = parent._ParseResults__name
          if not parentTag:
              parentTag = "ITEM"
          out = []
          for i, res in enumerate(parent._ParseResults__toklist):
              if isinstance(res, pp.ParseResults):
                  if i in namedItems:
                      child = as_tagged(res, namedItems[i])
                  else:
                      child = as_tagged(res, None)
                  out.append(child)
              else:
                  # individual token, see if there is a name for it
                  resTag = None
                  if i in namedItems:
                      resTag = namedItems[i]
                  if not resTag:
                      resTag = "ITEM"
                  child = (resTag, pp._ustr(res))
                  out += [child]
          return (parentTag, out)
  
      def combine_nested(opener, closer, content, name=None):
          r"""
          opener, closer, content = '(', ')', nest_body
          """
          import utool as ut  # NOQA
          ret1 = pp.Forward()
          # if opener == closer:
          #     closer = pp.Regex('(?<!' + re.escape(closer) + ')')
          _NEST = ut.identity
          #_NEST = pp.Suppress
          opener_ = _NEST(opener)
          closer_ = _NEST(closer)
  
          group = pp.Group(opener_ + pp.ZeroOrMore(content) + closer_)
          ret2 = ret1 << group
          if ret2 is None:
              ret2 = ret1
          else:
              pass
              #raise AssertionError('Weird pyparsing behavior. Comment this line if encountered. pp.__version__ = %r' % (pp.__version__,))
          if name is None:
              ret3 = ret2
          else:
              ret3 = ret2.setResultsName(name)
          assert ret3 is not None, 'cannot have a None return'
          return ret3
  
      # Current Best Grammar
      nest_body = pp.Forward()
      nest_expr_list = []
      for left, right in nesters:
          if left == right:
              # Treat left==right nestings as quoted strings
              q = left
              quotedString = pp.Group(q + pp.Regex(r'(?:[^{q}\n\r\\]|(?:{q}{q})|(?:\\(?:[^x]|x[0-9a-fA-F]+)))*'.format(q=q)) + q)
              nest_expr = quotedString.setResultsName('nest' + left + right)
          else:
              nest_expr = combine_nested(left, right, content=nest_body, name='nest' + left + right)
          nest_expr_list.append(nest_expr)
  
      # quotedString = Combine(Regex(r'"(?:[^"\n\r\\]|(?:"")|(?:\\(?:[^x]|x[0-9a-fA-F]+)))*')+'"'|
      #                        Regex(r"'(?:[^'\n\r\\]|(?:'')|(?:\\(?:[^x]|x[0-9a-fA-F]+)))*")+"'").setName("quotedString using single or double quotes")
  
      nonBracePrintables = ''.join(c for c in pp.printables if c not in ''.join(nesters)) + ' '
      nonNested = pp.Word(nonBracePrintables).setResultsName('nonNested')
      # nonNested = (pp.Word(nonBracePrintables) | pp.quotedString).setResultsName('nonNested')
      nonNested = nonNested.leaveWhitespace()
  
      # if with_curl and not with_paren and not with_brak:
      nest_body_input = nonNested
      for nest_expr in nest_expr_list:
          nest_body_input = nest_body_input | nest_expr
  
      nest_body << nest_body_input
  
      nest_body = nest_body.leaveWhitespace()
      parser = pp.ZeroOrMore(nest_body)
  
      debug_ = ut.VERBOSE
  
      if len(string) > 0:
          tokens = parser.parseString(string)
          if debug_:
              print('string = %r' % (string,))
              print('tokens List: ' + ut.repr3(tokens.asList()))
              print('tokens XML: ' + tokens.asXML())
          parsed_blocks = as_tagged(tokens)[1]
          if debug_:
              print('PARSED_BLOCKS = ' + ut.repr3(parsed_blocks, nl=1))
      else:
          parsed_blocks = []
      return parsed_blocks