def signup(request, form_class=SignupForm,
        template_name="account/signup.html", success_url=None):
    if success_url is None:
        success_url = get_default_redirect(request)
    if request.method == "POST":
        form = form_class(request.POST)
        if form.is_valid():
            username, password = form.save()
            if settings.ACCOUNT_EMAIL_VERIFICATION:
                return render_to_response("account/verification_sent.html", {
                    "email": form.cleaned_data["email"],
                }, context_instance=RequestContext(request))
            else:
                user = authenticate(username=username, password=password)
                auth_login(request, user)
                request.user.message_set.create(
                    message=_("Successfully logged in as %(username)s.") % {
                    'username': user.username
                })
                return HttpResponseRedirect(success_url)
    else:
        form = form_class()
    return render_to_response(template_name, {
        "form": form,
    }, context_instance=RequestContext(request))

class SignupForm(forms.Form):

    username = forms.CharField(label=_("Username"), max_length=30, widget=forms.TextInput())
    password1 = forms.CharField(label=_("Password"), widget=forms.PasswordInput(render_value=False))
    password2 = forms.CharField(label=_("Password (again)"), widget=forms.PasswordInput(render_value=False))

    if settings.ACCOUNT_REQUIRED_EMAIL or settings.ACCOUNT_EMAIL_VERIFICATION:
        email = forms.EmailField(
            label = _("Email"),
            required = True,
            widget = forms.TextInput()
        )
    else:
        email = forms.EmailField(
            label = _("Email (optional)"),
            required = False,
            widget = forms.TextInput()
        )

    confirmation_key = forms.CharField(max_length=40, required=False, widget=forms.HiddenInput())

    def clean_username(self):
        if not alnum_re.search(self.cleaned_data["username"]):
            raise forms.ValidationError(_("Usernames can only contain letters, numbers and underscores."))
        try:
            user = User.objects.get(username__iexact=self.cleaned_data["username"])
        except User.DoesNotExist:
            return self.cleaned_data["username"]
        raise forms.ValidationError(_("This username is already taken. Please choose another."))

    def clean(self):
        if "password1" in self.cleaned_data and "password2" in self.cleaned_data:
            if self.cleaned_data["password1"] != self.cleaned_data["password2"]:
                raise forms.ValidationError(_("You must type the same password each time."))
        return self.cleaned_data

    def save(self):
        username = self.cleaned_data["username"]
        email = self.cleaned_data["email"]
        password = self.cleaned_data["password1"]

        if self.cleaned_data["confirmation_key"]:
            from friends.models import JoinInvitation # @@@ temporary fix for issue 93
            try:
                join_invitation = JoinInvitation.objects.get(confirmation_key = self.cleaned_data["confirmation_key"])
                confirmed = True
            except JoinInvitation.DoesNotExist:
                confirmed = False
        else:
            confirmed = False

        # @@@ clean up some of the repetition below -- DRY!

        if confirmed:
            if email == join_invitation.contact.email:
                new_user = User.objects.create_user(username, email, password)
                join_invitation.accept(new_user) # should go before creation of EmailAddress below
                new_user.message_set.create(message=ugettext(u"Your email address has already been verified"))
                # already verified so can just create
                EmailAddress(user=new_user, email=email, verified=True, primary=True).save()
            else:
                new_user = User.objects.create_user(username, "", password)
                join_invitation.accept(new_user) # should go before creation of EmailAddress below
                if email:
                    new_user.message_set.create(message=ugettext(u"Confirmation email sent to %(email)s") % {'email': email})
                    EmailAddress.objects.add_email(new_user, email)
        else:
            new_user = User.objects.create_user(username, "", password)
            if email:
                new_user.message_set.create(message=ugettext(u"Confirmation email sent to %(email)s") % {'email': email})
                EmailAddress.objects.add_email(new_user, email)

        if settings.ACCOUNT_EMAIL_VERIFICATION:
            new_user.is_active = False
            new_user.save()

        return username, password # required for authenticate()