Question

I’m having trouble getting a simple Hello World app to work using Flask, MongoDB, and Python. The app is bombing when trying to import from the bson module. All modules were installed successfully via pip and I’m running in a virtualenv, so I’m not sure why I’m getting the error: ImportError: cannot import name BSON

Here is my sample app code:

import os
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 = Flask(__name__)

@app.route('/')
def hello():

    connection = Connection()
    # Get your DB
    db = connection.my_database
    # Get your collection
    cars = db.cars
    # Create some objects
    import datetime
    car = {"brand": "Ford",
           "model": "Mustang",
           "date": datetime.datetime.utcnow()}
    # Insert it
    cars.insert(car)
    json_docs = [json.dumps(doc, default=json_util.default) for doc in cars.find()]

    return json_docs


if __name__ == '__main__':
    # Bind to PORT if defined, otherwise default to 5000.
    port = int(os.environ.get('PORT', 5000))
    app.debug = True
    app.run(host='0.0.0.0', port=port)

I’m not sure how to go about debugging this or if there’s something I’m missing here.

Edit: results of pip freeze:

Flask==0.9
Jinja2==2.6
WTForms==1.0.2
Werkzeug==0.8.3
bson==0.3.3
distribute==0.6.28
mongo==0.2.0
pymongo==2.3
pytz==2012g
wsgiref==0.1.2

Edit2: Removed bson and pymongo, reran pip install pymongo. Complete trace now:

Traceback (most recent call last):
18:21:20 web.1  |   File ".../venv/lib/python2.7/site-packages/flask/app.py", line 1701, in __call__
18:21:20 web.1  |     return self.wsgi_app(environ, start_response)
18:21:20 web.1  |   File ".../venv/lib/python2.7/site-packages/flask/app.py", line 1689, in wsgi_app
18:21:20 web.1  |     response = self.make_response(self.handle_exception(e))
18:21:20 web.1  |   File ".../venv/lib/python2.7/site-packages/flask/app.py", line 1687, in wsgi_app
18:21:20 web.1  |     response = self.full_dispatch_request()
18:21:20 web.1  |   File ".../venv/lib/python2.7/site-packages/flask/app.py", line 1361, in full_dispatch_request
18:21:20 web.1  |     response = self.make_response(rv)
18:21:20 web.1  |   File ".../venv/lib/python2.7/site-packages/flask/app.py", line 1450, in make_response
18:21:20 web.1  |     rv = self.response_class.force_type(rv, request.environ)
18:21:20 web.1  |   File ".../venv/lib/python2.7/site-packages/werkzeug/wrappers.py", line 711, in force_type
18:21:20 web.1  |     response = BaseResponse(*_run_wsgi_app(response, environ))
18:21:20 web.1  |   File ".../venv/lib/python2.7/site-packages/werkzeug/test.py", line 818, in run_wsgi_app
18:21:20 web.1  |     app_iter = app(environ, start_response)
18:21:20 web.1  | TypeError: 'list' object is not callable

Answer 1

Try uninstalling the bson and pymongo packages and then reinstalling the pymongo package. pymongo installs its own bson package and I think you’ve overwritten it with the other bson package installation and that is probably what is causing your import error.

FYI:

• when you pip install pymongo it also installs bson but it does not ever print a message saying that it is install bson to your virtualenv site-packages
• also pymongo does not list bson as a dep
• also pip -v list does not show that bson is installed
• those bullet points IMO have some code smell (at least print a message stating you are installing bson)