import FreeCAD as App


def is_object_solid(obj):
    """If obj is solid return True"""
    if not isinstance(obj, FreeCAD.DocumentObject):
        return False

    if not hasattr(obj, 'Shape'):
        return False

    return obj.Shape.isClosed()

def addProperty():
    for obj in App.ActiveDocument().Objects:
        if is_object_solid(obj):