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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_snapshot(self):
 """Create snapshot if needed."""

        if self._snapshot is None:
            self._snapshot = self._get_session().snapshot(
                read_timestamp=self._read_timestamp,
                exact_staleness=self._exact_staleness,
                multi_use=True,
            )
            self._snapshot.begin()
        return self._snapshot