import hou
 
 
 def childCategory(node):
     """The name of the category of nodes this node contains, or ''.
 
     hou.Node.childTypeCategory() returns None for nodes that cannot have
     children, which is most of them below the object level.
     """
     category = node.childTypeCategory()
     return category.name() if category is not None else ''
 
 
 def collect_visible_nodes(nodes):
     """Display nodes of every visible SOP container reachable from `nodes`.
 
     Walks down through displayed object subnetworks, collecting the display
     node of each displayed SOP container. Takes and returns plain hou.Node.
     """
     stack = list(nodes)
     visible_nodes = []
 
     while stack:
         node = stack.pop()
         category = childCategory(node)
 
         if category == 'Sop' and node.isDisplayFlagSet():
             if node.type().name() == 'cam':
                 continue
             display_node = node.displayNode()
             if display_node is not None:
                 visible_nodes.append(display_node)
             continue
 
         if (category == 'Object'
                 and node.isSubNetwork()
                 and node.isDisplayFlagSet()):
             stack.extend(node.children())
 
     return visible_nodes