code: def update_field(self, action, field, value, max_tries=10):
          
          self._update_field(action, field, value, max_tries)
docs: Updates a field in the remote document. If a conflict exists,
          the document is re-fetched from the remote database and the update
          is retried.  This is performed up to ``max_tries`` number of times.
  
          Use this method when you want to update a single field in a document,
          and don't want to risk clobbering other people's changes to
          the document in other fields, but also don't want the caller
          to implement logic to deal with conflicts.
  
          For example:
  
          .. code-block:: python
  
              # Append the string 'foo' to the 'words' list of Document doc.
              doc.update_field(
                  action=doc.list_field_append,
                  field='words',
                  value='foo'
              )
  
          :param callable action: A routine that takes a Document object,
              a field name, and a value. The routine should attempt to
              update a field in the locally cached Document object with the
              given value, using whatever logic is appropriate.
              Valid actions are
              :func:`~cloudant.document.Document.list_field_append`,
              :func:`~cloudant.document.Document.list_field_remove`,
              :func:`~cloudant.document.Document.field_set`
          :param str field: Name of the field to update
          :param value: Value to update the field with
          :param int max_tries: In the case of a conflict, the number of retries
              to attempt