<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def post(self, request, *args, **kwargs):
 """ Returns POST response. :param request: the request instance. :rtype: django.http.HttpResponse. """

        form        = None
        link_type   = int(request.POST.get('link_type', 0))

        if link_type == Link.LINK_TYPE_EMAIL:
            form = EmailLinkForm(**self.get_form_kwargs())
        elif link_type == Link.LINK_TYPE_EXTERNAL:
            form = ExternalLinkForm(**self.get_form_kwargs())

        if form:
            if form.is_valid():
                return self.form_valid(form)
            else:
                return self.form_invalid(form)
        else:
            raise Http404()