code: def addColumn(self, columnName, dtype, defaultValue):
          
          model = self.tableView.model()
  
          if model is not None:
              model.addDataFrameColumn(columnName, dtype, defaultValue)
  
          self.addColumnButton.setChecked(False)
docs: Adds a column with the given parameters to the underlying model
  
          This method is also a slot.
          If no model is set, nothing happens.
  
          Args:
              columnName (str): The name of the new column.
              dtype (numpy.dtype): The datatype of the new column.
              defaultValue (object): Fill the column with this value.