code: def _parse_attr(cls, value, package_dir=None):
          
          attr_directive = 'attr:'
          if not value.startswith(attr_directive):
              return value
  
          attrs_path = value.replace(attr_directive, '').strip().split('.')
          attr_name = attrs_path.pop()
  
          module_name = '.'.join(attrs_path)
          module_name = module_name or '__init__'
  
          parent_path = os.getcwd()
          if package_dir:
              if attrs_path[0] in package_dir:
                  # A custom path was specified for the module we want to import
                  custom_path = package_dir[attrs_path[0]]
                  parts = custom_path.rsplit('/', 1)
                  if len(parts) > 1:
                      parent_path = os.path.join(os.getcwd(), parts[0])
                      module_name = parts[1]
                  else:
                      module_name = custom_path
              elif '' in package_dir:
                  # A custom parent directory was specified for all root modules
                  parent_path = os.path.join(os.getcwd(), package_dir[''])
          sys.path.insert(0, parent_path)
          try:
              module = import_module(module_name)
              value = getattr(module, attr_name)
  
          finally:
              sys.path = sys.path[1:]
  
          return value
docs: Represents value as a module attribute.
  
          Examples:
              attr: package.attr
              attr: package.module.attr
  
          :param str value:
          :rtype: str