def setKeyExtractMethod(self, keyExtractMethod=None):
        """ key extract from line for sort method:
            def f(line):
                return line[1:3], line[5:10]
        """                
        if keyExtractMethod is None:
            self._getKey = lambda line: line
        else:
            self._getKey = keyExtractMethod
 key extract from line for sort method:
            def f(line):
                return line[1:3], line[5:10]
        
recipes/Python/415581_big_file_sorting/recipe-415581.py