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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 _build_one(self, req, output_dir, python_tag=None):
 """Build one wheel. :return: The filename of the built wheel, or None if the build failed. """

        # Install build deps into temporary directory (PEP 518)
        with req.build_env:
            return self._build_one_inside_env(req, output_dir,
                                              python_tag=python_tag)