How to get POSTed json in Flask?

I'm trying to build a simple API using Flask, in which I now want to read some POSTed JSON. I do the post with the PostMan Chrome extension, and the JSON I post is simply {"text":"lalala"}. I try to read the JSON using the following method:

    @app.route('/api/add_message/<uuid>', methods=['GET', 'POST'])
    def add_message(uuid):
        content = request.json
        print content
        return uuid

On the browser it correctly returns the uuid I put in the GET, but on the console, it just prints out None (where I expect it to print out the {"text":"lalala"}. Does anybody know how I can get the posted JSON from within the Flask method?

You need to set the request content type to application/json for the .json property to work; it'll be None otherwise. See the Flask Request documentation:

If the mimetype is application/json this will contain the parsed JSON data. Otherwise this will be None.

Flask 0.10 added the request.get_json() method, and you should use that method instead of the .json property. You can tell the method to skip the content type requirement by setting force=True.

Note that if an exception is raised at this point (possibly resulting in a 400 Bad Request response), your JSON data is invalid. It is in some way malformed; you may want to check it with a JSON validator.