On Thu, Jan 31, 2013 at 5:53 PM, Hugo Arts <hugo.yoshi at gmail.com> wrote: > >>>> a = ([], []) >>>> a[0] += [1] > TypeError: 'tuple' object does not support item assignment >>>> a > ([1], []) Yep, storing the result fails for a read-only subscript or attribute (e.g. a property without fset), but only after the in-place op executes. Solution: don't do that. ;)