class_docstr: Python class for ordered set.
  Code taken from https://github.com/buyalsky/ordered-hash-set/tree/5198b23e01faeac3f5398ab2c08cb013d14b3702.
docstr: Function to add an element to do set if it does not exit.
  
  :param element: element to be added.
docstr_tok: ["Function","to","add","an","element","to","do","set","if","it","does","not","exit",".",":","param","element",":","element","to","be","added","."]
code: def add(self, element):
      """
      Function to add an element to do set if it does not exit.
  
      :param element: element to be added.
      """
      if self._start is None:
          self._start = element
  
      if element not in self._set.keys():
          self._set[element] = None
          if len(self._set) > 1:
              self._set[self._end] = element
          self._end = element
  
file_path: dowhy/dowhy/utils/ordered_set.py
label_desc: Use image node_id 2 for calling the OrderedSet obj's underlying member method code with example usage: obj.add(element) without return types