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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 _dir_additions(self):
 """ add the string-like attributes from the info_axis. If info_axis is a MultiIndex, it's first level values are used. """

        additions = {c for c in self._info_axis.unique(level=0)[:100]
                     if isinstance(c, str) and c.isidentifier()}
        return super()._dir_additions().union(additions)