Short snippet to create output folders of a Write Node in Nuke.

write_makedirs.py

import os

n = nuke.selectedNode()
if n.Class() != 'Write':
    nuke.message('No Write Node selected')
else:
    filepath = os.path.dirname(n['file'].evaluate())
    proxypath = os.path.dirname(n['proxy'].evaluate())
    
    question = 'Yes = create normal file path:\n'
    question += filepath
    question += '\n\n'
    question += 'No = create proxy file path\n'
    question += proxypath
    
    createfileorproxy = nuke.ask(question)
    path = filepath if createfileorproxy else proxypath
    
    if not os.path.isdir(path):
      os.makedirs(path)