{"action":"created","issue":{"url":"https://api.github.com/repos/SciTools/iris/issues/1889","labels_url":"https://api.github.com/repos/SciTools/iris/issues/1889/labels{/name}","comments_url":"https://api.github.com/repos/SciTools/iris/issues/1889/comments","events_url":"https://api.github.com/repos/SciTools/iris/issues/1889/events","html_url":"https://github.com/SciTools/iris/issues/1889","id":124464031,"number":1889,"title":"GRIB derived keys","user":{"login":"marqh","id":1557321,"avatar_url":"https://avatars.githubusercontent.com/u/1557321?v=3","gravatar_id":"","url":"https://api.github.com/users/marqh","html_url":"https://github.com/marqh","followers_url":"https://api.github.com/users/marqh/followers","following_url":"https://api.github.com/users/marqh/following{/other_user}","gists_url":"https://api.github.com/users/marqh/gists{/gist_id}","starred_url":"https://api.github.com/users/marqh/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/marqh/subscriptions","organizations_url":"https://api.github.com/users/marqh/orgs","repos_url":"https://api.github.com/users/marqh/repos","events_url":"https://api.github.com/users/marqh/events{/privacy}","received_events_url":"https://api.github.com/users/marqh/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":4,"created_at":"2015-12-31T11:54:51Z","updated_at":"2016-01-08T11:32:46Z","closed_at":null,"body":"The GRIB loader uses \r\n```\r\ngribapi.grib_skip_computed(keys_itr)\r\n```\r\nhttps://github.com/SciTools/iris/blob/master/lib/iris/fileformats/grib/_message.py#L295\r\n\r\nat grib api version 12 this also returned computed keys, which are then used in GDT40\r\n- https://github.com/SciTools/iris/blob/master/lib/iris/fileformats/grib/_load_convert.py#L902\r\n- https://github.com/SciTools/iris/blob/master/lib/iris/fileformats/grib/_load_convert.py#L971\r\n\r\nThis 'bug' has been fixed, so the code used for GDT40 no longer runs, as the keys are not available\r\n\r\nWe need to decide whether to relax the constraint on using computed keys or refactor the relevant code to not use them\r\n\r\nwhich approach is preferred?\r\nmark"},"comment":{"url":"https://api.github.com/repos/SciTools/iris/issues/comments/169972799","html_url":"https://github.com/SciTools/iris/issues/1889#issuecomment-169972799","issue_url":"https://api.github.com/repos/SciTools/iris/issues/1889","id":169972799,"user":{"login":"pp-mo","id":2089069,"avatar_url":"https://avatars.githubusercontent.com/u/2089069?v=3","gravatar_id":"","url":"https://api.github.com/users/pp-mo","html_url":"https://github.com/pp-mo","followers_url":"https://api.github.com/users/pp-mo/followers","following_url":"https://api.github.com/users/pp-mo/following{/other_user}","gists_url":"https://api.github.com/users/pp-mo/gists{/gist_id}","starred_url":"https://api.github.com/users/pp-mo/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/pp-mo/subscriptions","organizations_url":"https://api.github.com/users/pp-mo/orgs","repos_url":"https://api.github.com/users/pp-mo/repos","events_url":"https://api.github.com/users/pp-mo/events{/privacy}","received_events_url":"https://api.github.com/users/pp-mo/received_events","type":"User","site_admin":false},"created_at":"2016-01-08T11:32:46Z","updated_at":"2016-01-08T11:32:46Z","body":"> I don't think we should limit ourselves to coded keys blindly\r\n\r\nIIRC the key reason is that we got burnt in the past by the definitions of computed keys changing (or vanishing) with gribapi version changes, so we took a solemn oath not to use them...\r\nFor instance, we  had things change return type at one point : [old issue comment](https://github.com/SciTools/iris/pull/452#discussion_r3954403)\r\nDoes that  sound at all  familiar @rhattersley @marqh, or I am out of order ?"}}