Bug 338098 added support for defining object properties using GObject.Property. In pygtk I was creating child properties using a dictionary, for example:
   
    __gchild_properties__ = {
        'weight': (GObject.TYPE_FLOAT,
                   'item weight',
                   'item weight',
                   0,  # min
                   1,  # max
                   .2,  # default
                   GObject.ParamFlags.READWRITE
                  ),
    }

and then:
    for index, (name, pspec) in enumerate(six.iteritems(DockPaned.__gchild_properties__)):
    pspec = list(pspec)
    pspec.insert(0, name)
    Gtk.ContainerClass.install_child_property(DockPaned, index + 1, tuple(pspec))

Unfortunately with PyGObject this gives a TypeError: argument pspec: Expected GObject.ParamSpec, but got tuple

There needs to be a way to create child properties through install_child_property. What if we defined these properties using a new GObject.ChildProperty solution similar to what was added for other normal properties?