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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 _installed_packages(self) -> Generator[str, None, None]: """Extract installed packages as list from `package.json`."""

        with (self._build_dir / 'package.json').open('r') as f:
            packages = json.load(f)
        yield from packages['dependencies'].keys()