My app won't return render_template('404.html')

Question

I've double- and triple-checked my code and it's exactly as Kenneth writes it out, imported abort and all, but I'm still not getting the 404.html template. Any idea what could explain this? Here's the relevant code, copy-pasted out of Sublime:

Follow view:

@app.route('/follow/<username>')
@login_required
def follow(username):
    try:
        to_user = models.User.get(models.User.username**username)
    except models.DoesNotExist:
        abort(404)
    else:
        try:
            models.Relationship.create(
                from_user=g.user._get_current_object(),
                to_user=to_user
            )
        except models.IntegrityError:
            pass
        else:
            flash("You're now following {}!".format(to_user.username), "success")
    return redirect(url_for('stream', username=to_user.username))

Unfollow view:

@app.route('/unfollow/<username>')
@login_required
def unfollow(username):
    try:
        to_user = models.User.get(models.User.username**username)
    except models.DoesNotExist:
        abort(404)
    else:
        try:
            models.Relationship.get(
                from_user=g.user._get_current_object(),
                to_user=to_user
            ).delete_instance()
        except models.IntegrityError:
            pass
        else:
            flash("You've unfollowed {}!".format(to_user.username), "success")
    return redirect(url_for('stream', username=to_user.username))

Stream/User stream view:

@app.route('/stream')
@app.route('/stream/<username>')
def stream(username=None):
    template = 'stream.html'
    if username and username != current_user.username:
        try:
            user = models.User.select().where(
                models.User.username**username).get()
        except models.DoesNotExist:
            abort(404)
        else:
            stream = user.posts.limit(100)
    else:
        stream = current_user.get_stream().limit(100)
        user=current_user
    if username:
        template = 'user_stream.html'
    return render_template(template, stream=stream, user=user)

not_found() view:

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

404.html:

{% extends "layout.html" %}

{% block content %}

<h1>404</h1>

<p>Sorry, that page doesn't exist.</p>

<p><a href="{{ url_for('index') }}">Try again</a></p>

{% endblock %}

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Adam Cameron

Adam Cameron

My app won't return render_template('404.html')