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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 get_pk_index(self, collection):
 """Return the primary key index for a given collection. :param collection: the collection for which to return the primary index :returns: the primary key index of the given collection """

        cls = self.collections[collection]

        if not cls.get_pk_name() in self.indexes[collection]:
            self.create_index(cls.get_pk_name(), collection)
        return self.indexes[collection][cls.get_pk_name()]