.. _about-responses:

About Responses
---------------

The return value from a view function is automatically converted into a
response object for you.  If the return value is a string it's converted
into a response object with the string as response body, a ``200 OK``
status code and a :mimetype:`text/html` mimetype.  The logic that Flask applies to
converting return values into response objects is as follows:

1.  If a response object of the correct type is returned it's directly
    returned from the view.
2.  If it's a string, a response object is created with that data and the
    default parameters.
3.  If a tuple is returned the items in the tuple can provide extra
    information.  Such tuples have to be in the form ``(response, status,
    headers)`` or ``(response, headers)`` where at least one item has
    to be in the tuple.  The ``status`` value will override the status code
    and ``headers`` can be a list or dictionary of additional header values.
4.  If none of that works, Flask will assume the return value is a
    valid WSGI application and convert that into a response object.

If you want to get hold of the resulting response object inside the view
you can use the :func:`~flask.make_response` function.

Imagine you have a view like this::

    @app.errorhandler(404)
    def not_found(error):
        return render_template('error.html'), 404

You just need to wrap the return expression with
:func:`~flask.make_response` and get the response object to modify it, then
return it::

    @app.errorhandler(404)
    def not_found(error):
        resp = make_response(render_template('error.html'), 404)
        resp.headers['X-Something'] = 'A value'
        return resp