pyqgis - How to run Processing qgis:extractbylocation?

I try to use the processing 'qgis:extractbylocation' in QGIS 2.8.2 from the QGIS algorithm provider.

import processing
# import the layers by a given uri
inputlayer = QgsVectorLayer(uriTr.uri(), "inputlayer", "postgres")
intersectlayer = QgsVectorLayer(uriOSM.uri(), "intersectlayer", "postgres")

# initialize a predicate instance
pred_intersects = processing.core.parameters.ParameterGeometryPredicate(enabledPredicates = 'intersects')

# run the processing
processing.runalg('qgis:extractbylocation', inputlayer, intersectlayer, pred_intersects, None)

However I get the following error:

Traceback (most recent call last):
    File "", line 1, in 
    File "~/.qgis2/python/plugins/processing/tools/general.py", line 71, in runalg
        alg = Processing.runAlgorithm(algOrName, None, *args)
    File "~/.qgis2/python/plugins/processing/core/Processing.py", line 317, in runAlgorithm
        if not param.setValue(args[i]):

    File "~/.qgis2/python/plugins/processing/core/parameters.py", line 829, in setValue
        elif len(value) == 0:
AttributeError: ParameterGeometryPredicate instance has no attribute '__len__'

The algorithm needs the following inputs

processing.alghelp("qgis:extractbylocation")
     ALGORITHM: Extract by location
     INPUT 
     INTERSECT 
     PREDICATE 

     OUTPUT 

ParameterGeometryPredicate is described here: https://fossies.org/dox/qgis-2.8.2/classprocessing_1_1core_1_1parameters_1_1ParameterGeometryPredicate.html

How do I need to initialize a correct instance of the ParameterGeometryPredicate class?

Answer

The predicate is u'intersects'. For more than one predicate use an array like "[u'within',u'intersects']"

The full command is

processing.runalg('qgis:extractbylocation', inputlayer, intersectlayer, u'intersects', None)

The possible arguments for the predicates are:

[u'disjoint',u'intersects',u'contains',u'equals',u'touches',u'overlaps',u'within',u'crosses']

The similar algorithm selectbylocation is used like

processing.runalg('qgis:selectbylocation', inputlayer, intersectlayer, u'intersects', 0)