"Bill Chiles" <billchi@microsoft.com> wrote:
For Common Lispers and probably Schemers, Python has some surprising semantics around scope and lifetime extent of variables. Three that leap out at me are:
One thing to remember is that Python is not Scheme/Lisp. It borrows some ideas from Scheme/Lisp, but that borrowing does not necessitate a it also use a completely equivalent scoping mechanism. From what I have been hearing about Python 2.6, and 3.0, the three "surprises" you describe are not going to be "fixed" (with respect to expected Scheme/Lisp semantics). Feel free to argue as to why they should be "fixed" in Py3k (unless Guido says, "you're dreaming"), but please do so in the py3k list. - Josiah
* function parameters with default values are NOT new bindings for each invocation, so a default value of [] changes if you destructively modify this list object in the function * loop variables are NOT distinct lexical variables. The binding gloms on to a variable in the function's scope, both changing that lexical binding and not creating a new one for the loop (that goes away when the loop's scope ends) * loop variables are NOT distinct bindings per iteration, leading to the surprising results below