[Python-Dev] once [was: Simple Switch statementZ] (original) (raw)
Jim Jewett jimjjewett at gmail.com
Wed Jun 28 20:38:04 CEST 2006
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On 6/28/06, Guido van Rossum <guido at python.org> wrote:
On 6/28/06, Jim Jewett <jimjjewett at gmail.com> wrote: > On 6/28/06, Guido van Rossum <guido at python.org> wrote:
> > def indexfunctions(n): > > return [(lambda i=i: i) for i in range(n)]
> > which works but has the disadvantage of returning a list of functions > > of 0 or 1 argument
> Another alternative might be letting functions get at themselves, > rather than just their names. (Methods can save attributes on self, > but functions are out of luck if someone else reused their name.)
This has been proposed before. Because (as you say) the function name is not generally safe to use, there's no good API; all proposals I've seen are ugly.
It basically requires a reserved word.
def f(a, b="key", __func__.extra=i):
if __func__.extra < 43: ...And anyway this would be way too complex for the little lambda I was using as an example.
def index_functions(n):
return [(lambda __func__.i=i: i) for i in range(n)]> > Capture expressions outside functions would be illegal or > > limited to compile-time constant expressions (unless someone has a > > better idea).
> At a minimum, it should be able to capture the expression's current > value at load-time, which might well involve names imported from > another module.
I'm not sure what you mean by "load time".
The first time a module is imported. When running from a .py file, this is the same as compile time.
I didn't say compile-time because I don't want it frozen permanently for the entire installation when the .pyc file is first written.
> > A capture expression inside "if 0:" would still be > > captured to simplify the semantics (unless the compiler can prove that > > it has absolutely no side effects).
> Running code that was guarded by "if 0:" sounds like a really bad idea.
Assuming that the compiler will treat code guarded by "if 0:" different from code guarded by "if x:" where you happen to know that x is always false sounds like a really bad idea too.
The indent rules mean it will never be reached, so it can't have side effects. I expect that "if 0: push_the_red_button" will not risk pushing the red button.
Freezing a once-variable at funcdef time means that I have to look inside the indent after all. "If 0:" is just an especially bad special case.
-jJ
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