code: def addDependency(self, item):
          
          if item in self._dependencies:
              return
          
          viewItem = XGanttDepItem(self, item)
          
          self._dependencies[item]        = viewItem
          item._reverseDependencies[self] = viewItem
          
          self.syncDependencies()
docs: Creates a dependency for this item to the next item.  This item will
          be treated as the source, the other as the target.
          
          :param      item | <QGanttWidgetItem>