from qgis.utils import iface
from PyQt4.QtCore import QVariant
_ID_FIELD = 'RS'
_NAME_FIELD = 'GEN'
_PLZ_FIELD = 'plz'
_NEW_ID_FIELD = 'PARENT_ID'
_NEW_NAME_FIELD = 'PARENT_NAME'
Land_layer = iface.mapCanvas().layer(1)
PLZ_layer = iface.mapCanvas().layer(0)
# Create 2 new fields in the layer that will hold the list of neighbors and sum
# of the chosen field.

#PLZ_layer.startEditing()
#PLZ_layer.dataProvider().addAttributes(
#        [QgsField(_NEW_ID_FIELD, QVariant.String),
#         QgsField(_NEW_NAME_FIELD, QVariant.Int)])
#PLZ_layer.updateFields()

## Create a dictionary of all features
PLZ_feature_dict = {f.id(): f for f in PLZ_layer.getFeatures()}
Land_feature_dict = {f.id(): f for f in Land_layer.getFeatures()}
# Build a spatial index
index = QgsSpatialIndex()
print 'PLZ Layer: %s' % PLZ_layer.name()
print 'Landkreis Layer: %s' % Land_layer.name()

for f in Land_feature_dict.values():
    index.insertFeature(f)
    print 'Inserting %s in Landkreis index' % f[_NAME_FIELD]

for f in PLZ_feature_dict.values():
    print 'Working on %s' % f[_PLZ_FIELD]
    geom = f.geometry()
    intersect_ids = index.intersects(geom.boundingBox())
    for id in intersect_ids:
        tempf = Land_feature_dict[id]
        print 'got parent Landkreis %s' % tempf[_NAME_FIELD]

intersect_ids = index.intersects(geom.boundingBox())


Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "//VAIMUCO9/G114305$/Anwendungsdaten/Desktop/PLZ/ContainerFinder.py", line 34, in  <module>
    intersect_ids = index.intersects(geom.boundingBox())
AttributeError: 'NoneType' object has no attribute 'boundingBox'