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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 id_to_symbol(self, entrez_id):
 """Gives the symbol for a given entrez id)"""


        entrez_id = str(entrez_id)
        if entrez_id not in self.ids_to_symbols:
            m = 'Could not look up symbol for Entrez ID ' + entrez_id
            raise Exception(m)
        return self.ids_to_symbols[entrez_id]