Python: Deleted Node Check

[galagast]

On the shell:

1. I stored a hou.node("/obj/geo1") onto a variable obj.

2. Then I deleted the geo1 object in the scene.

3. I check the obj variable, it now returns an error as expected:

>>> obj
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "C:/PROGRA~1/SIDEEF~1/HOUDIN~1.393/houdini/python2.7libs\hou.py", line 8015, in __repr__
    def __repr__(*args): return _hou.ObjNode___repr__(*args)
ObjectWasDeleted: Attempt to access an object that no longer exists in Houdini.

My question now is, how do I check if a node was deleted? Or if it is still valid?

I'm looking for a command similar to MaxScript's isValidNode <var>: Returns true if <var> is a node value, and the node has not been deleted. Otherwise, it returns false.
 

I'm planning to use it on an if statement like so:

if isValidNode(obj):

[Atom]

Holding a reference to a node, beyond it's current scope, is not wise. Simply fetch the expected node at the top of the code. If it exists, you will have a valid node to operate upon.

There are some status functions associated with nodes, however, use print dir(obj) to review them. But if the node has been deleted those functions will not be available.

 

Otherwise create your own test with a try/except to determine if the node is still valid.

Edited March 15, 2016 by Atom

[galagast]

Thank you for the response Atom. I'll use print dir(obj) to study more of the associated functions of the node.

 

Yes, my current workaround for now was I created a separate function with a try/except inside it to determine a node's validity.

[galagast]

In relation to the question, is there a way to check if a provided path is valid?

 

Say I have an input string of:

foo = "/geo/box1"

I then would later use that for:

obj = hou.node(foo)

But before I do, is there a way to check if the foo string path is a valid path on the current session?

[willow wafflebeard]

import os.path
obj = ""
nodename = os.path.basename(foo)
kids = map( lambda x: x.name(), node.children() )
if nodename in kids:
   obj = hou.node(foo)

could this suffice?

im sure you can use filter() straight after map()

 

or you can just do:

raise hou.Error("no such node in object") or raise ValueError("no such node in object") somewhere in the code

 

edit: i noticed its a path

Edited March 16, 2016 by willow wafflebeard

[anim]

...before I do, is there a way to check if the foo string path is a valid path on the current session?

hou.node() will return None if the path is invalid

so you can straight away just do:

path = "/any/path"
node = hou.node(path)
if node:
    print "node %s exists and it's a %s" % (node.path(), node.type().name())
else:
    print "node %s doesn't exist" % path

Edited March 16, 2016 by anim

[galagast]

Thanks guys!

@Willow: Those are new to me, I'm reading up on lambda, map and filter now. I will definitely consider its usage during my forays in python.

@Tomas, awesome, I did end up doing that after a couple of tests last night Glad I was on the right path.