Menu class supporting the Presenter

menu.py

#!/usr/bin/python

from xml.dom.minidom import parse
import presenter
from xmlutils import remove_whitespace_nodes

class Menu :
  """ a menu represents a menu and its current status 
     
     attributes
       name - the name of the menu
       root  - the base of the menu
       current  - the current item in the menu  

  """
  def __init__(self,name) :
    """ create a menu object from an XML   file 

    file is the name of an XML file which conforms to the schema: 

    DOM parse  is used to parse the XML and build the tree of XML objects. 
    whitespace text nodes are deleted 
  
    """
    self.name = name
    doc = parse(name +"_menu.xml")
    self.root = doc.firstChild  #  menu 
    remove_whitespace_nodes(self.root)  
    self.current = self.root

  def move (self,action) :
    """Using action, move the current position in the menu left ,right, up or down the tree
 
       left and right wrap round
       down goes down a level if there are sub item or is ignored
       up goes up a level until the containing Document is reached, when None is returned

    """
    if self.current is None :
      pass
    elif action == "left" : # previous item
      sib = self.current.previousSibling
      if sib is None :
          self.current= self.current.parentNode.lastChild
      else :
          self.current = sib
    elif action =="down" :  # down one level if there are children
      if self.current.hasChildNodes():
          self.current = self.current.firstChild
      else :
          pass
    elif action == "right" : # next item 
      sib = self.current.nextSibling
      if sib is None:
         self.current = self.current.parentNode.firstChild
      else :
         self.current = sib
    elif action == "up" : # back up one level
      parent = self.current.parentNode 
      if parent is self.root.ownerDocument:
         self.current = None
      else :
         self.current = parent
    else :
      """ invalid action """
      print action + " not recognised "
      self.current = None

  def run(self, visit) :
    """ run walks through the menu using the keys, executing the supplied visit function as each item is visited

      the visit function will return a Item DOM object

    """
    visit(self.current)
    for key in presenter.read_key() :
       self.move(key)
       if self.current is None :
          exit()
       else :
          visit(self.current)