def append_mag(data=bpy.data, use_fake_user=False):
    in_sockets = [
        {'name': 'Vector',
         'data_type': 'NodeSocketVector'}
    ]

    out_sockets = [
        {'name': 'Magnitude',
         'default_value': 1.0,
         'min_value': 0.0}
    ]

    # Create group.
    mag_group = append_group_node(name='Mag', data=data, use_fake_user=use_fake_user, in_sockets=in_sockets, out_sockets=out_sockets)

    # Create vector math nodes.
    nodes = mag_group.nodes
    dotp = append_vec_math_node(nodes, operation='DOT_PRODUCT')
    sqrt = append_math_node(nodes, operation='POWER', b_default=0.5)

    # Link nodes.
    links = mag_group.links
    links.new(sqrt.inputs[0], dotp.outputs[1])

    # Link to group inputs.
    mag_input = mag_group.nodes['Group Input']
    links.new(dotp.inputs[0], mag_input.outputs[0])
    links.new(dotp.inputs[1], mag_input.outputs[0])

    # Link to group outputs.
    mag_output = mag_group.nodes['Group Output']
    links.new(mag_output.inputs[0], sqrt.outputs[0])

    return mag_group