request.user.message_set
was deprecated in Django 1.2 and has been removed since Django 1.4, the message framework should be used instead.
from django.contrib import messages
# messages.add_message(request, level, message, extra_tags="", fail_silently=False)
messages.add_message(request, messages.INFO, "Your Message")
Alternatively, you can use one of the shortcut functions:
from django.contrib import messages
messages.debug(request, "Your Message")
messages.info(request, "Your Message")
messages.success(request, "Your Message")
messages.warning(request, "Your Message")
messages.error(request, "Your Message")
Messages can then be rendered on the template with:
{% if messages %}
<ul class="messages">
{% for message in messages %}
<li{% if message.tags %} class="{{ message.tags }}"{% endif %}>{{ message }}</li>
{% endfor %}
</ul>
{% endif %}