Recursive function going infinite and I can't see why.

[Gregory Piñero]

Hi,

Would anyone be able to tell me why my function below is getting stuck
in infinite recusion?
Maybe I'm just tired and missing something obvious?

def replace_within_node(node,oldnode,newnode):
    if node is oldnode:
        return newnode
    else:
        for varname,value in node.__dict__.items():
            node.__dict__[varname]=replace_within_node(value,oldnode,newnode)
        return node

At the end of this email I pasted the whole text of the sample code in
case it would help to see it in context or maybe step through it?

--
Gregory Piñero
Chief Innovation Officer
Blended Technologies
(www.blendedtechnologies.com)


#This is the code that's causing my problem:
#----------------------------------------------------------------------

import random
import sys

class Test_Class:
        pass
class Node:
    def __init__(self):
        self.arg0=0
        self.arg1=0
        self.arg2=0
        self.arg3=0

def snip(node):
    prob_of_returning_this_node=.4
    if random.random()<=prob_of_returning_this_node:
        return node
    else:
        if hasattr(node,'__dict__') and len(node.__dict__)>0:
            return snip(random.choice(node.__dict__.values()))
        else:
            return node

def replace_within_node(node,oldnode,newnode):
    if node is oldnode:
        return newnode
    else:
        if hasattr(node,'__dict__'):
            for varname,value in node.__dict__.items():
               
node.__dict__[varname]=replace_within_node(value,oldnode,newnode)
        return node

def generate_random_program(currdepth,mindepth=2,maxdepth=4):
    node=Node()
    if currdepth==maxdepth:
        return node
    else:
        node=Node()
        for varname,value in node.__dict__.items():
            node.__dict__[varname]=generate_random_program(currdepth+1,mindepth,maxdepth)
        return node

def breed(father,mother):
    #want to take subtree from each input parameter and swap them.
    snip_from_mother=snip(mother.program)
    snip_from_father=snip(father.program)
    program_for_father=replace_within_node(father.program,snip_from_father,snip_from_mother)
    program_for_mother=replace_within_node(mother.program,snip_from_mother,snip_from_father)
    return program_for_father,program_for_mother

if __name__=='__main__':
    dragons=[Test_Class() for i in range(10)]
    for dragon in dragons:
        dragon.program=generate_random_program(0)
    for i in range(100):
        breed(dragons[0],dragons[1])