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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 update_elements(dst_pyxb, src_pyxb, el_list):
 """Copy elements specified in ``el_list`` from ``src_pyxb`` to ``dst_pyxb`` Only elements that are children of root are supported. See SYSMETA_ROOT_CHILD_LIST. If an element in ``el_list`` does not exist in ``src_pyxb``, it is removed from ``dst_pyxb``. """

    invalid_element_set = set(el_list) - set(SYSMETA_ROOT_CHILD_LIST)
    if invalid_element_set:
        raise ValueError(
            'Passed one or more invalid elements. invalid="{}"'.format(
                ', '.join(sorted(list(invalid_element_set)))
            )
        )
    for el_str in el_list:
        setattr(dst_pyxb, el_str, getattr(src_pyxb, el_str, None))