def raison(request, individu_id):
    # code here

HttpResponseRedirect('%i/raison/' % individu_id)

from django.core.urlresolvers import reverse


def index(request):
   # code here
   if ...:
       next = reverse("raison", kwargs={"individu_id": individu_id})
       return HttpResponseRedirect(next)

from django.shortcuts import redirect


def index(request):
   # code here
   if ...:
       return redirect("raison", individu_id=individu_id)