object is not JSON serializable

Question

I'm having some trouble with Mongodb and Python (Flask).

I have this api.py file, and I want all requests and responses to be in JSON, so I implement as such.

# # Imports #  from datetime import datetime from flask import Flask from flask import g from flask import jsonify from flask import json from flask import request from flask import url_for from flask import redirect from flask import render_template from flask import make_response import pymongo from pymongo import Connection from bson import BSON from bson import json_util  # # App Create #  app = Flask(__name__) app.config.from_object(__name__)  # # Database #  # connect connection = Connection() db = connection['storage'] units = db['storage']   # # Request Mixins #  @app.before_request def before_request():     #before     return  @app.teardown_request def teardown_request(exception):     #after     return   # # Functions #  def isInt(n):     try:         num = int(n)         return True     except ValueError:         return False  def isFloat(n):     try:         num = float(n)         return True     except ValueError:         return False  def jd(obj):     return json.dumps(obj, default=json_util.default)  def jl(obj):     return json.loads(obj, object_hook=json_util.object_hook)  # # Response #  def response(data={}, code=200):     resp = {         "code" : code,         "data" : data     }     response = make_response(jd(resp))     response.headers['Status Code'] = resp['code']     response.headers['Content-Type'] = "application/json"     return response   # # REST API calls #  # index @app.route('/') def index():     return response()  # search @app.route('/search', methods=['POST']) def search():      return response()  # add @app.route('/add', methods=['POST']) def add():     unit = request.json     _id = units.save(unit)     return response(_id)  # get @app.route('/show', methods=['GET']) def show():     import pdb; pdb.set_trace();     return response(db.units.find())  # # Error handing #  @app.errorhandler(404) def page_not_found(error):     return response({},404)   # # Run it! #  if __name__ == '__main__':     app.debug = True     app.run() 

The problem here is json encoding data coming to and from mongo. It seems I've been able to "hack" the add route by passing the request.json as the dictionary for save, so thats good... the problem is /show. This code does not work... When I do some logging I get

TypeError: <pymongo.cursor.Cursor object at 0x109bda150> is not JSON serializable 

Any ideas? I also welcome any suggestions on the rest of the code, but the JSON is killing me.

Thanks in advance!

Answer 1

While @ErenGüven shows you a nice manual approach to solving this json serializing issue, pymongo comes with a utility to accomplish this for you. I use this in my own django mongodb project:

import json from bson import json_util  json_docs = [] for doc in cursor:     json_doc = json.dumps(doc, default=json_util.default)     json_docs.append(json_doc) 

Or simply:

json_docs = [json.dumps(doc, default=json_util.default) for doc in cursor] 

And to get them back from json again:

docs = [json.loads(j_doc, object_hook=json_util.object_hook) for j_doc in json_docs] 

The helper utilities tell json how to handle the custom mongodb objects.