def convert_py_namespace_to_header_filename(python_namespace):
    """Convert a Python namespace to the name of the root C++ header file.

    Parameters
    ----------
    python_namespace : `str`
        A string describing a Python namespace. For example,
        ``'lsst.example'``.

    Returns
    -------
    header_filename : `str`
        Filename of the root header file.
    """
    parts = python_namespace.split('.')
    return parts[-1] + '.h'
