parameters: (self, item, cookie)
docstring: Returns the previous child of an item.
  
          :param `item`: an instance of :class:`TreeListItem`;
          :param `cookie`: a parameter which is opaque for the application but is necessary
           for the library to make these functions reentrant (i.e. allow more than one
           enumeration on one and the same object simultaneously).
  
          :note: This method returns ``None`` if there are no further siblings.
docstring_summary: Returns the previous child of an item.
docstring_tokens: Returns the previous child of an item .
function: def GetPrevChild(self, item, cookie):
          """
          Returns the previous child of an item.
  
          :param `item`: an instance of :class:`TreeListItem`;
          :param `cookie`: a parameter which is opaque for the application but is necessary
           for the library to make these functions reentrant (i.e. allow more than one
           enumeration on one and the same object simultaneously).
  
          :note: This method returns ``None`` if there are no further siblings.
          """
  
          children = item.GetChildren()
  
          if cookie >= 0:            
              return children[cookie], cookie-1
          else:        
              # there are no more of them
              return None, cookie
function_tokens: def GetPrevChild ( self , item , cookie ) : children = item . GetChildren ( ) if cookie >= 0 : return children [ cookie ] , cookie - 1 else : # there are no more of them return None , cookie