The variables (names) 'f' and 'g' are reused every time the loop iterates.
You are correct that doing an explicit 'del' within the loop would
presumably prevent the magic mutation-not-binding behavior under
discussion. I still don't want the behavior, but I admit that's a pretty
easy way to be more explicit if it were added.
On Thu, Jun 27, 2019, 11:56 AM Steven D'Aprano <st...@pearwood.info> wrote:
> On Thu, Jun 27, 2019 at 09:55:53AM -0400, David Mertz wrote:
> > On Thu, Jun 27, 2019 at 9:13 AM Steven D'Aprano <st...@pearwood.info>
> wrote:
> >
> > > The only risk here is if your refactoring does something silly, such as
> > > reusing a variable which overrides assignment:
> >
> > How would you propose to write this code without reusing a variable?
> >
> > def frobnicate(data):
> > stuff = []
> > for datum in data:
> > f = process_the(data)
> > g = munge_result(f)
> > stuff.append(g)
> > return stuff
>
> Rewrite it in what way? What problem are you trying to solve?
>
> If you just want to "flush" the local variables at the end of each loop
> and ensure that they have been deleted, you can explicitly delete them:
>
> del f, g, datum
>
> If you are talking about the kind of refactoring Chris was talking
> about, I don't see any reason, or opportunity, to do that. If anything,
> you could reverse the refactoring:
>
> def frobnicate(data):
> stuff = []
> for datum in data:
> stuff.append(munge_result(process_the(datum)))
> return stuff
>
> which leads to the obvious comprehension:
>
> return [munge_result(process_the(datum)) for datum in data]
>
> which allows us to eliminate the variable re-use:
>
> return list(map(lambda x: munge_result(process_the(x)), data))
>
>
> [...]
> > Without
> > looking at the source code in `process_the()` we have no way of knowing
> > whether `f` is being bound to a new object each time or some completely
> > different arbitrary action.
>
> That's exactly the situation right now. Functions can perform arbitrary
> actions and return the same object each time.
>
> def process_the(arg):
> print("do something arbitrary")
> return None
>
>
> --
> Steven
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