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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 get_lib_filename(category, name):
 """ Get a filename of a built-in library file. """

    base_dir = os.path.dirname(os.path.abspath(__file__))
    if category == 'js':
        filename = os.path.join('js', '{0}.js'.format(name))
    elif category == 'css':
        filename = os.path.join('css', '{0}.css'.format(name))
    elif category == 'html':
        filename = os.path.join('html', '{0}.html'.format(name))
    else:
        raise ValueError("Unknown category")
    return os.path.join(base_dir, 'lib', filename)