id,node_id,number,state,locked,title,user,body,created_at,updated_at,closed_at,merged_at,merge_commit_sha,assignee,milestone,draft,head,base,author_association,auto_merge,repo,url,merged_by
698447552,MDExOlB1bGxSZXF1ZXN0Njk4NDQ3NTUy,5640,closed,0,Fix performance bug from cftime import,3801015,"<!-- 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.
",2021-07-28T07:44:06Z,2021-09-29T16:34:00Z,2021-09-29T16:05:57Z,2021-09-29T16:05:57Z,434090909dfad3e77df2488ab957ceb650045285,,,0,8619ad90df578909b16d7f4adeb1534b009d59ef,c4f3a9ee7c20dfe9b5364b880204a13753d8ef2c,CONTRIBUTOR,,13221727,https://github.com/pydata/xarray/pull/5640,