foo.py

from flask import Flask, stream_with_context, json, Response


app = Flask(__name__)

@app.route('/')
def index():
    def gen():
        yield json.dumps({'foo': 'spam'})
        yield json.dumps({'bar': 'eggs'})
    return Response(stream_with_context(gen()), content_type='application/json')

if __name__ == '__main__':
    app.run(debug=True)

output

% curl -v 127.0.0.1:5000
* About to connect() to 127.0.0.1 port 5000 (#0)
*   Trying 127.0.0.1...
* connected
* Connected to 127.0.0.1 (127.0.0.1) port 5000 (#0)
> GET / HTTP/1.1
> User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8x zlib/1.2.5
> Host: 127.0.0.1:5000
> Accept: */*
> 
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Content-Type: application/json
< Connection: close
< Server: Werkzeug/0.9 Python/2.7.3
< Date: Thu, 13 Jun 2013 18:52:43 GMT
< 
* Closing connection #0
{"foo": "spam"}{"bar": "eggs"}%