myalgorithm.py

from qgis.core import QgsApplication
from processing.core.Processing import Processing
from processing.tools import general

from pywps.Process import WPSProcess
from types import StringType

class Process(WPSProcess):
     def __init__(self):
         WPSProcess.__init__(self,
              identifier       = "myalgorithm",
              title            = "Title",
              version          = "1",
              storeSupported   = "false",
              statusSupported  = "false",
              abstract         = "Abstract....")

         self.result = self.addLiteralOutput(identifier = "result", title = "result", type = StringType)

     def execute(self):
         qgis = QgsApplication([], False)
         qgis.setPrefixPath("C:/Program Files/QGIS 2.18/apps/qgis", True)
         qgis.initQgis()
         # Processing.initialize()
         # general.runalg('qgis:extractnodes', 'C:/river.shp', 'C:/output.shp')
         qgis.exitQgis()
         self.result.setValue("End")