I am coding a node for animation nodes. I need to initialize a set of variables so I can use them, but I need to do it in such a way that they won't be refreshed (reset to the default value) every time I send an output to the node.

I probably want to define the variables before my create(self) method, so it won't refresh every time I send/receive I/O from the execute(self,a,b,...) method.

I have this:

enter image description here def create(self) new.Input(...) new.Input(...) new.Output(...) etc...

def execute(self,a,b,etc..)
   loops involving variables.

Where do I define my variables, and what is the syntax for calling them to check or change values without resetting them to their default start settings?


1 Answer 1


You can define such variable outside of the node class and call it as you would call a global variable. Take the Text File Reader node for example, it defines a cache dictionary to cache file reads, the cache is initially defined outside of the class as:

cache = {}

class TextFileReaderNode(bpy.types.Node, AnimationNode):
    bl_idname = "an_TextFileReaderNode"
    bl_label = "Text File Reader"

And it assign and read the cache in the execute function normally:

with open(path, "r", encoding = encoding) as f:
    data = f.read()
    cache[key] = (lastModification, data)

You can also use the node identifier as a key in the dictionary to have a per-node variables. For instance, if you want a variable xBounce for every node, create an empty dictionary called xBounce and in the execution function, set its value using xBounce[self.identifier] = something and retrieve its value using xBounce.get(self.identifier, 0) where zero is the default value

  • $\begingroup$ I tried declaring three integer variables before the node itself, as you have shown here, but I still get a referenced before assignment error. I don't know how to show my code here in the comments, or I would add that to this question." Can you suggest what is going wrong? $\endgroup$
    – NullNaught
    Nov 29, 2018 at 13:31
  • $\begingroup$ @NullNaught Please add the code to the question. $\endgroup$
    – Omar Emara
    Nov 29, 2018 at 14:30
  • $\begingroup$ When I try to copy and paste, I get "866 characters too long." I don't know how to append my screenshot. I will try adding it as an edit to my question. $\endgroup$
    – NullNaught
    Nov 29, 2018 at 14:40
  • $\begingroup$ @NullNaught It seems Python assumes the variable is in the local scope. You should probably declare it as a global variable, see this answer. $\endgroup$
    – Omar Emara
    Nov 29, 2018 at 15:13
  • $\begingroup$ Can you tell me, is there any way to achieve the same thing without a global variable? I can't use two such nodes at the same time, when I would like to be able to. $\endgroup$
    – NullNaught
    Nov 30, 2018 at 7:47

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