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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def message_compose(request, recipients=None, compose_form=ComposeForm, success_url=None, template_name="umessages/message_form.html", recipient_filter=None, extra_context=None):
 """ Compose a new message :recipients: String containing the usernames to whom the message is send to. Can be multiple username by seperating them with a ``+`` sign. :param compose_form: The form that is used for getting neccesary information. Defaults to :class:`ComposeForm`. :param success_url: String containing the named url which to redirect to after successfull sending a message. Defaults to ``userena_umessages_list`` if there are multiple recipients. If there is only one recipient, will redirect to ``userena_umessages_detail`` page, showing the conversation. :param template_name: String containing the name of the template that is used. :param recipient_filter: A list of :class:`User` that don"t want to receive any messages. :param extra_context: Dictionary with extra variables supplied to the template. **Context** ``form`` The form that is used. """

    initial_data = dict()

    if recipients:
        username_list = [r.strip() for r in recipients.split("+")]
        recipients = [u for u in get_user_model().objects.filter(username__in=username_list)]
        initial_data["to"] = recipients

    form = compose_form(initial=initial_data)
    if request.method == "POST":
        form = compose_form(request.POST)
        if form.is_valid():
            requested_redirect = request.GET.get(REDIRECT_FIELD_NAME,
                                                 request.POST.get(REDIRECT_FIELD_NAME, False))

            message = form.save(request.user)
            recipients = form.cleaned_data['to']

            if userena_settings.USERENA_USE_MESSAGES:
                messages.success(request, _('Message is sent.'),
                                 fail_silently=True)

            # Redirect mechanism
            redirect_to = reverse('userena_umessages_list')
            if requested_redirect: redirect_to = requested_redirect
            elif success_url: redirect_to = success_url
            elif len(recipients) == 1:
                redirect_to = reverse('userena_umessages_detail',
                                      kwargs={'username': recipients[0].username})
            return redirect(redirect_to)

    if not extra_context: extra_context = dict()
    extra_context["form"] = form
    extra_context["recipients"] = recipients
    return render(request, template_name, extra_context)