[Python-Dev] 2.5 and beyond (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Sat Jul 1 08:15:29 CEST 2006

Giovanni Bajo wrote:

a = [] for i in range(10): ... a.append(lambda: i) ...

print [x() for x in a] [9, 9, 9, 9, 9, 9, 9, 9, 9, 9] This subtle semantic of lambda is quite confusing, and still forces people to use the "i=i" trick.

This has nothing to do with the semantics of lambda! It's because Python's for-loop doesn't put its control variable in a new scope, the way Scheme's equivalent construct does.

That's what needs to be addressed to fix this problem. I've made a suggestion about that before, but Guido rejected it, so I won't repeat it here.

-- Greg

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