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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 pseudo_with_symbol(self, symbol, allow_multi=False):
 """ Return the pseudo with the given chemical symbol. Args: symbols: String with the chemical symbol of the element allow_multi: By default, the method raises ValueError if multiple occurrences are found. Use allow_multi to prevent this. Raises: ValueError if symbol is not found or multiple occurences are present and not allow_multi """

        pseudos = self.select_symbols(symbol, ret_list=True)
        if not pseudos or (len(pseudos) > 1 and not allow_multi):
            raise ValueError("Found %d occurrences of symbol %s" % (len(pseudos), symbol))

        if not allow_multi:
            return pseudos[0]
        else:
            return pseudos