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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 _private_notes2marc(self, key, value):
 """Populate the ``595`` MARC key. Also populates the `595_H` MARC key through side effects. """

    def _is_from_hal(value):
        return value.get('source') == 'HAL'

    if not _is_from_hal(value):
        return {
            '9': value.get('source'),
            'a': value.get('value'),
        }

    self.setdefault('595_H', []).append({'a': value.get('value')})