Python futures : How do I get the json from a future object in Tornado?

Question

This is a post handler :

handler.py

from imports import logic

@gen.coroutine
def post(self):
    data = self.request.body.decode('utf-8')
    params = json.loads(data)
    model_id= params['model_id']
    logic.begin(model_id)

The logic object is imported from imports.py where it is instantiated from an imported class Logic

imports.py :

import Models
import Logic

class Persist(object):
    def getModel(self, model_id):
        model = Models.findByModelId(model_id)
        return model


persist = Persist()
logic = Logic(persist)

logic.py

class Logic(object):
    def __init__(self, persist):
        self._persist = persist

    def begin(self, model_id):
         model = self._persist.get_model(model_id)
         print ("Model from persist : ")
         print (model)

the get_model method uses Models which makes a DB query and returns the future object :

model.py:

from motorengine.document import Document

class Models(Document):
    name = StringField(required=True)

def findByModelId(model_id):
    return Models.objects.filter(_id=ObjectId(model_id)).find_all()

This prints a future object in console :

<tornado.concurrent.Future object at 0x7fbb147047b8>

How can I convert it to json ?

score 4 · Answer 1 · answered Aug 17 '15 at 02:53

To resolve a Future into an actual value, yield it inside a coroutine:

@gen.coroutine
def begin(self, model_id):
     model = yield self._persist.get_model(model_id)
     print ("Model from persist : ")
     print (model)

Any function that calls a coroutine must be a coroutine, and it must yield the return value of the coroutine to get its return value:

@gen.coroutine
def post(self):
    data = self.request.body.decode('utf-8')
    params = json.loads(data)
    model_id = params['model_id']
    model = yield logic.begin(model_id)
    print(model)

More advanced coding patterns don't need to follow these rules, but to begin with, follow these basic rules.

For more information about calling coroutines from coroutines, see Refactoring Tornado Coroutines.

Python futures : How do I get the json from a future object in Tornado?

1 Answers1