id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
954574705,MDExOlB1bGxSZXF1ZXN0Njk4NDQ3NTUy,5640,Fix performance bug from cftime import,3801015,closed,0,,,11,2021-07-28T07:44:06Z,2021-09-29T16:34:00Z,2021-09-29T16:05:57Z,CONTRIBUTOR,,0,pydata/xarray/pulls/5640,"<!-- Feel free to remove check-list items aren't relevant to your change -->

No functional change, just removes a terrible perfomance bug when cftime isn't installed - previously calls to `.sel` would search your whole python path for trying to import cftime, leading to progams of mine taking 10% of time just doing this against a slow filesystem.

Tests all pass localy.
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