ManyToMany field with newforms

class Edittalkform(forms.Form):
    def __init__(self, *args, **kwargs):
            self.fields['speaker'].choices = [(chld.id, 
            chld.username) for chld in Delegate.objects.all()]
 
    title = forms.CharField(max_length=250,
                                            label=_("Talk Title")
                                            )

    speaker = forms.MultipleChoiceField(label=_("Speaker(s)"),
                                            choices=()
                                            )

            
@user_passes_test(lambda u: u.is_anonymous()==False ,login_url="/web/login/")  
@transaction.commit_on_success
def edittalk(request,id):
    if request.POST:
        form = Edittalkform(request.POST)
        if form.is_valid():
            fm = form.cleaned_data
            delgid = Delegate.objects.get(username=request.user).id
            if str(delgid) not in fm['speaker']:
                    form.errors['speaker'] = [_("Your own username\
                    is missing from the list of speakers")]
            if not form.errors:
                newtalk.title = fm['title']
                newtalk.save()
                # remove all the previous speakers
                newtalk.speaker.clear()
                for spk in fm['speaker']:
                    newtalk.speaker.add(Delegate.objects.get(pk=int(spk)))
                return HttpResponseRedirect("/web/talks/" )
    else:
        tlk = Talk.objects.get(pk=id)
        data = {
                        'title': tlk.title,
                        'speaker': [p.id for p in tlk.speaker.all()],
                        }
        
        form = Edittalkform(data)
    return render_to_response("web/edittalk.html",
                              {'form':form,
                               'request':request
                               })