pyqgis - Go through items in a composer legend (QGIS 2.6)

I'm trying to develop a plugin in QGIS 2.6, which opens a composer, add a map and a legend, and (among other things) adjusts the legend.

Is there a way to go through items in a composer legend with PyQgis? What I'd want in the end is to change the item name, depending on the type of item (group, raster ...).

Here is my code:

for legend in self.composition.items():

    if isinstance(i,QgsComposerLegend):
        legend.setAutoUpdateModel(True)
        legend.setLegendFilterByMapEnabled(True)            
        for item in legend.items():
            if item.itemtype() == QgsComposerLegendItem.GroupItem:
                groupItem.setUserText() = 'another text'

Qgis answers that QgsComposerLegend has not attribute called "items" (which I expected). I looked for a property to iterate on legend items, and I have not found it in the API documentation nor in web searches.