For review: PEP 308 - If-then-else expression

[Andrew Koenig]

Andrew> Hmmm, well, here's an ugly trick,

Andrew>     col = [None, cols[max(i, 0)]][i>=0]

Yes, indeed, it's ugly -- especially because if i<=0 and len(cols)==0,
it fails where the original would have succeeded.

Andrew> and here's another

Andrew>    col = [[None] + cols][max(i+1, 0)]

This one is O(len(cols)) where the original is O(1).

Andrew> but neither have the grace of

Andrew>    col = None if i < 0 else cols[i]

Right.

Andrew> OTOH, I still say this is easier to debug, because I can do

Andrew>          if i < 0:
Andrew>              print "Negative?", i
Andrew>              col = None
Andrew>          else:
Andrew>              print "i", i, "neighbors", cols[max(i-1, 0):i+1]
Andrew>              col = cols[i]

Yes indeed.  The flip side comes when you do something like this a bunch
of times and your function no longer fits on the screen.

-- 
Andrew Koenig, ark at research.att.com, http://www.research.att.com/info/ark