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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 potcar_symbols(self):
 """ List of POTCAR symbols. """

        elements = self.poscar.site_symbols
        potcar_symbols = []
        settings = self._config_dict["POTCAR"]

        if isinstance(settings[elements[-1]], dict):
            for el in elements:
                potcar_symbols.append(settings[el]['symbol']
                                      if el in settings else el)
        else:
            for el in elements:
                potcar_symbols.append(settings.get(el, el))

        return potcar_symbols