response = HttpResponse(content_type='text/csv')  # Format response as a CSV
filename = 'some_file_name' + '.csv'
response['Content-Disposition'] = 'attachment; filename="' + filename + '"'  # Name the CSV response
df.to_csv(response, encoding='utf-8', index=False)
return response

if df is None or df.shape[0] ==0:
    messages.warning(request, 'failure message.')
else:
     messages.success(request, 'success message.')

{% if messages %}
    <ul class="messages">
        {% for message in messages %}
            <li{% if message.tags %} class="{{ message.tags }}"{% endif %} id="export_messages">{{ message }}</li>
        {% endfor %}
    </ul>
{% endif %}

<form class="default_form" method="POST" action="my_action">