import nuke
import nukescripts
import threading

class tmpPanel(nukescripts.PythonPanel):

    def __init__(self):

        nukescripts.PythonPanel.__init__(self, "tmp panel")
        self.writes = nuke.Enumeration_Knob("writes", "writes", [node.name() for node in self.getWrites()])
        self.render = nuke.PyScript_Knob("render", "render")

        for i in [self.writes, self.render]:
            self.addKnob(i)

    def knobChanged(self, knob):

        if knob is self.render:
            self.renderWrites()

    def renderWrites(self):

        writeNode = self.writes.value()
        node = nuke.toNode(writeNode)
        threading.Thread(target = nuke.execute, args= (node , 1, 5, 1)).start()

    def getWrites(self):

        return (node for node in nuke.allNodes() if node.Class() == "Write")

tmpPanel().show()