Antoon Pardon wrote: > Well maybe because as far as I understand the same kind of logic > can be applied to something like > > lst[f()] += foo > > In order to decide that this should be equivallent to > > lst[f()] = lst[f()] + foo. > > But that isn't the case.
Because, surprisingly enough, Python tends to evaluate expressions only once each time they're invoked. In this case, [] is being used to get an item and set an item -- therefore, it /has/ to be invoked twice -- once for __getitem__, and once for __setitem__. Likewises, lst appears once, and it is used once -- the name gets looked up once (which leads to a += 1 problems if a is in an outer scope). f() also appears once -- so to evaluate it more trhan one time is odd, at best. If you know very much about modern lisps, it's similar to the difference between a defun and a defmacro. -- http://mail.python.org/mailman/listinfo/python-list
