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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 resolver(self):
 """jsonschema RefResolver object for the base schema."""

        if self._resolver is not None:
            return self._resolver
        if self._schema_path is not None:
            # the documentation for ref resolving
            # https://github.com/Julian/jsonschema/issues/98
            # https://python-jsonschema.readthedocs.org/en/latest/references/
            self._resolver = SchemaRefResolver(
                'file://' + self._schema_path + '/', self.schema)
        else:
            self._resolver = SchemaRefResolver.from_schema(self.schema)
        return self._resolver