For similar questions that you are asked in your former posts, I think that you want to know how to visualize them (centroids) at the Map Canvas. In this case you need, e.g., one memory layer. Modifying your code to:
layerName = "INTERIOR"
layer = QgsMapLayerRegistry.instance().mapLayersByName(layerName)
epsg = layer.crs().postgisSrid()
uri = "Point?crs=epsg:" + str(epsg) + "&field=id:integer""&index=yes"
mem_layer = QgsVectorLayer(uri,
prov = mem_layer.dataProvider()
for f in layer.getFeatures():
feat = QgsFeature()
pt = f.geometry().centroid().asPoint()
i += 1
After running it at the Python Console of QGIS, with a shapefile with the same name as yours, I got:
Now, they are visible.