def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def add_category():
    form = CategoryForm()

    if form.validate_on_submit():
        form.save()
        flash(_("Category added."), "success")
        return redirect(url_for("management.forums"))

    return render_template("management/category_form.html", form=form,
                           title=_("Add Category"))