Question

I am trying to use memcache with ProtoRPC to speed up some process (Google App Engine with Python). To simplify question I used Hello World example, and modified it a little bit. Here is my version:

from protorpc import messages
from protorpc import remote
from protorpc.wsgi import service

from google.appengine.api import memcache

class HelloRequest(messages.Message):
  my_name = messages.StringField(1, required=True)

class ElementOfArrayResponse(messages.Message):
  value=messages.IntegerField(1)

class HelloResponse(messages.Message):
  hello = messages.StringField(1, required=True)
  list = messages.MessageField(ElementOfArrayResponse, 2, repeated=True)

class HelloService(remote.Service):
  @remote.method(HelloRequest, HelloResponse)
  def hello(self, request):
    response = memcache.get(request.my_name)

    if response is None:
      list = []
      for i in range(7):
        list.append(SomeElementResponse(value=i))
      response = HelloResponse(hello='Hello there, %s!' % request.my_name, list=list)
      memcache.set(request.my_name,response)
    return response

app = service.service_mappings([('/hello.*', HelloService)])

But, unfortunately, this code returns an error which is: ERROR 2013-01-12 17:17:31,081 service.py:196] Encountered unexpected error from ProtoRPC method implementation: PicklingError (Can't pickle <type 'weakref'>: attribute lookup __builtin__.weakref failed).

However, when I use almost the same code with original HelloResponse, memcache works great.

So, what am I doing wrong?

Answer 1

two things, it looks like your memcache key is a List object (want to make sure you’re aware of that). next to your code, you’ll have to serialize the message object when putting / getting out of the memcache api.

here’s a rewrite:

from protorpc import remote
from protorpc import messages
from protorpc import protojson
from protorpc.wsgi import service
from google.appengine.api import memcache


class HelloRequest(messages.Message):
  my_name = messages.StringField(1, required=True)

class ElementOfArrayResponse(messages.Message):
  value=messages.IntegerField(1)

class HelloResponse(messages.Message):
  hello = messages.StringField(1, required=True)
  list = messages.MessageField(ElementOfArrayResponse, 2, repeated=True)

class HelloService(remote.Service):
  @remote.method(HelloRequest, HelloResponse)
  def hello(self, request):
    response = memcache.get(request.my_name)
    if response:
      # decode the value to a message..
      response = protojson.decode_message(HelloResponse, response)
    else:
      list = []
      for i in range(7):
        list.append(SomeElementResponse(value=i))
      response = HelloResponse(hello='Hello there, %s!' % request.my_name, list=list)
      # encode the message to a serializable format..
      value = protojson.encode_message(message)
      memcache.set(request.my_name, value)
    return response

app = service.service_mappings([('/hello.*', HelloService)])