Altering composer label items in QGIS with Python

I'm only new to QGIS and Python so this may exists already, and hopefully be easy to do.

What I'm hoping to do sometime in the future is build a map book generator using QGIS as the base. In order to do this I need to be able to select all the labels in the composer and replace some tags, so something like $NAME$ would replace with a variable the user has set at runtime.

I have been having a look at the QGIS APIs [and source] but just can't seem to get it to do what I need. The code I have so far:

composerList = self.iface.activeComposers()
if(len(composerList) < 1):
      return


composerView = composerList[0]
composition = composerView.composition()
if(composition is None):
      return

for item in composition.selectedComposerItems():
//Need to check for QgsComposerLabel type and update the text.

I'm stuck when it comes to checking the type of the current item in Python, selectedComposerItems() just returns each item as a QgsComposerItem and calling displayText() fails because it doesn't exists on the type QgsComposerItem.

I have tried the following code but it crashes QGIS when it hits a legend or scale bar:

for item in composition.selectedComposerItems():
    try:
        item.__class__ = qgis.core.QgsComposerLabel
        if item.displayText() == "$NAME$":
            print "I found one"
            item.setText("Hello World")
    except:
        print "Fail"

The idea was to just try setting __class__ on every item as qgis.core.QgsComposerLabel and if it throws an exception then I know it's not a label, but at the moment if it hits a legend or scale bar it crashes QGIS which is not good.

Answer

type(item).__name__

should return 'QgsComposerLabel', but only returns 'QgsComposerItem'.

There's now a ticket in QGIS Trac.