code: def setColumnMapper(self, columnName, callable):
          
          columnName = nativestring(columnName)
          if ( callable is None and columnName in self._columnMappers ):
              self._columnMappers.pop(columnName)
              return
          
          self._columnMappers[nativestring(columnName)] = callable
docs: Sets the mapper for the given column name to the callable.  The inputed
          callable should accept a single argument for a record from the tree and
          return the text that should be displayed in the column.
          
          :param      columnName | <str>
                      callable   | <function> || <method> || <lambda>