On 01/26/2014 09:59 AM, francis wrote: > On 01/26/2014 03:42 AM, Raymond Hettinger wrote: >> >> I think that is an over-simplification. The argument unpacking was handy >> in a number of situations where *args wouldn't suffice: >> >> lambda (px, py), (qx, qy): ((px - qx) ** 2 + (py - qy) ** 2) ** 0.5 >> >> IIRC, the original reason for the change was that it simplified the >> compiler a bit, >> not that it was broken or not useful. > I'm not sure if that's applicable or other issues arise with: > > def fn(*p): px,py,qx,qy = p; return ((px - qx) ** 2 + (py - qy) ** 2) ** > 0.5
[Dropping some whitespace to get things to all fit on one line] The goal is to call fn as: fn((1, 1), (2, 2)) So, in 2.7: >>> def fn((px, py), (qx, qy)): ... return ((px-qx)**2+(py-qy)**2)**0.5 ... >>> fn((1, 1), (2, 2)) 1.4142135623730951 >>> The nearest equivalent in 3.3 (also works in 2.7): >>> def fn(p, q): ... (px, py), (qx, qy) = p, q ... return ((px-qx)**2+(py-qy)**2)**0.5 ... >>> fn((1, 1), (2, 2)) 1.4142135623730951 For a lambda in 3.3, you're out of luck because you can't do the assignment. There, the best you can do is: >>> fn = lambda p, q: ((p[0]-q[0])**2+(p[1]-q[1])**2)**0.5 >>> fn((1, 1), (2, 2)) 1.4142135623730951 Which isn't quite so readable as the equivalent lambda in 2.7: >>> fn = lambda (px, py),(qx, qy):((px-qx)**2+(py-qy)**2)**0.5 >>> fn((1, 1), (2, 2)) 1.4142135623730951 As someone pointed out, it's not quite the same when you do your own tuple unpacking, but it's probably close enough for most cases. Eric. _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
