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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 find_sphinx_build_dir():
 """ Find build subfolder within sphinx docs directory. This is called by :func:`commit_docs` if keyword arg ``built_docs`` is not specified on the command line. """

    build = glob.glob('**/*build/html', recursive=True)
    if not build:
        raise RuntimeError("Could not find Sphinx build directory automatically")
    build_folder = build[0]

    return build_folder