def rename_targets(self):
        ''' This method will check for each t in self.targets, if t exists.
            If it does, t will be renamed to be t+".partial". This method is
            called whenever this task halts unexpectedly or in error.
        '''
        for f in self.targets:
            if(os.path.exists(f)):
                os.rename(f, f + '.partial')