def read_config_file(libname):
    """
    Extract library locations from a configuration file.

    Parameters
    ----------
    libname : str
        One of either 'openjp2' or 'openjpeg'

    Returns
    -------
    path : None or str
        None if no location is specified, otherwise a path to the library
    """
    filename = glymurrc_fname()
    if filename is None:
        # There's no library file path to return in this case.
        return None

    # Read the configuration file for the library location.
    parser = ConfigParser()
    parser.read(filename)
    try:
        path = parser.get('library', libname)
    except (NoOptionError, NoSectionError):
        path = None
    return path