如何在Django中提交后清除表单字段

I've this:

我是这样的：

def profile(request, username):
if request.method == 'POST':
    if request.user.is_authenticated():
        new_message = Message(author = request.user)
        form = MessagesForm(request.POST, instance = new_message)
    else:
        form = MessagesForm(request.POST)
    if form.is_valid():
        form.save()
else:
    to_user = User.objects.get(username = username)
    form = MessagesForm(initial = {'user': to_user.pk})


return render(request, "profile.html", {'username': username, 'form': form, 'messages': messages})
def profile(request, user