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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 write_cache(self):
 """Writes the cache to disk as JSON."""

        doc = {
            '__format__': 1,
            'dependencies': self._cache,
        }
        with open(self._cache_file, 'w') as f:
            json.dump(doc, f, sort_keys=True)