pip install flask-mongoengine

from flask import Flask
from flask.ext.mongoengine import MongoEngine
 
app = Flask(__name__)
app.config.from_pyfile('the-config.cfg')
db = MongoEngine(app)

Or, if you are setting up your database before your app is initialized….

from flask import Flask
from flask.ext.mongoengine import MongoEngine
db = MongoEngine()
...
app = Flask(__name__)
app.config.from_pyfile('the-config.cfg')
db.init_app(app)

app.config['MONGODB_SETTINGS'] = {
    'db': 'project1',
    'host': '192.168.1.35',
    'port': 12345,
    'username':'webapp',
    'password':'pwd123'
}

app.config['MONGODB_DB'] = 'project1'
app.config['MONGODB_HOST'] = '192.168.1.35'
app.config['MONGODB_PORT'] = 12345
app.config['MONGODB_USERNAME'] = 'webapp'
app.config['MONGODB_PASSWORD'] = 'pwd123'