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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _update_dirs_on_base(self):
        '''Fill up the names of dirs based on the contents of 'base'.'''
        if self._dirs['base'] != None:
            for d in self._predefined_dir_names:
                dstr = d
                #if d == "s2":
                #    dstr = '.'+d
                self._dirs[d] = os.path.join(self._dirs['base'], dstr)