Performing PUT , PATCH in python eve application returns , The method is not allowed for the requested URL
At first glance, I would say that the URL you are hitting (http://127.0.0.1:5000/puburl/) looks like a resource (collection) endpoint while PUT is a document (item) endpoint. That's why you are adding it to item_methods and not to resource_methods. You want to hit something like http://127.0.0.1:5000/puburl/<id> in order for PUT to work.
I think the problem is that the etag has to be in the headers with clause 'If-Match' = etag.
You can look more information on "Data Integrity and Concurrency Control" in http://python-eve.org/features.html