a syntax error with string casting in jinja

templates/index.html

@@ -18,7 +18,7 @@
 				<li class="pull-right">{{ valuedeletebtn(('announcements',msg.id,'deleted')) }}</li>
 				<li class="pull-right" style="padding-right: 5px;">
 					{% if not msg.visible %}
-						<a href="{{ url_for('edit', prefix='announcements.'+str(msg.id|string)+'.', ref=request.url, visible=1) }}" class="btn btn-primary">Veröffentlichen</a>
+						<a href="{{ url_for('edit', prefix='announcements.'+msg.id|string+'.', ref=request.url, visible=1) }}" class="btn btn-primary">Veröffentlichen</a>
 					{% elif msg.time_expire and msg.time_expire < datetime.now() %}
 						<a href="#" class="btn btn-danger disabled">Abgelaufen</a>
 					{% elif msg.time_publish and msg.time_publish > datetime.now() %}