use inheritance, not composition

[feth]

that's a feeling @GaelVaroquaux has.

[feth]

coded in the train, will push later. The quick n dirty implementation patch is less than 30 lines long

[GaelVaroquaux]

Awesome. Wanna see the patch :)

[feth]

Hm, that estimation was wrong :)

25 insertions, 18 deletions

[feth]

And I pushed to master instead of "composition"... well it's early in the morning