filecache: use try-except for faster __dict__ lookup Python function call is slow, and the cost could be significant here. $ hg perfrevset 'branch(tip)' -R mercurial (orig) wall 0.139511 comb 0.140000 user 0.140000 sys 0.000000 (best of 66) (this) wall 0.114195 comb 0.110000 user 0.110000 sys 0.000000 (best of 81)