Nuke editable dropdown ui

so i kept trying and got some direction now i what i am stuck into is changing the value in text box when pulldown_knob value is changed, here is what i have so far

import nukescripts
if nuke.env["gui"]:
   class PromptName(nukescripts.PythonPanel):
      def __init__(self, *args):
         self.readNodeLst = args
         nukescripts.PythonPanel.__init__( self, "Name for Backdrop", "namePrompt" ) = nuke.EvalString_Knob( "name", "Name:" )
         self.readNodes = nuke.Pulldown_Knob("pulldown",'nodeNames', self.retDict())
      def retDict(self):
            readNodeDict = {}
            for eachReadNode in self.readNodeLst:
                readNodeDict[eachReadNode] = self.setNameValue()
            return readNodeDict

# The next function shows the dialog as a modal dialog. Doing this automatically adds the 'OK' and 'Cancel' buttons to the dialog.
      def showModalDialog( self ):
         result = nukescripts.PythonPanel.showModalDialog(self)
         if result:

      def setNameValue(self):

# The following function is called testModalPanel and tests whether the dialog works.
   def testModalPanel():
      obj = PromptName("Hello","Hello2")
      #return PromptName().showModalDialog("Hello")
# This last line calls the test function that then displays the dialog.

i keep getting error saying:
Traceback (most recent call last):
File “<string>”, line 34, in <module>
File “<string>”, line 30, in testModalPanel
File “<string>”, line 8, in init
File “<string>”, line 16, in retDict
File “<string>”, line 26, in setNameValue
AttributeError: ‘PromptName’ object has no attribute ‘readNodes’

or how should i get the value of selected item in a pull down menu…?