Em sáb., 27 de jun. de 2020 às 11:12, Richard Damon < Richard@damon-family.org> escreveu:
On 6/27/20 5:36 AM, Stephen J. Turnbull wrote:
Richard Damon writes:
I thought _ was also commonly used as:
first, -, last = (1, 2, 3)
as a generic don't care about assignment.
It is. But there are other options (eg, 'ignored') if '_' is used for translation in the same scope.
I guess since the above will create a local, so not overwrite a 'global' function _ for translations, so the above usage works as long as that function (or whatever namespace you are in) doesn't use _ for translations.
Exactly.
As long as the bindings in match also make the symbol a local (which seems reasonable) then you would get a similar restriction.
It's quite different. First, it surely won't make other symbols match-local. Of course there will be times when you do all the work inside the match statement. But often you'll want to do bindings in a match statement, then use those outside. The second problem is that this use of '_' isn't optional. It's part of the syntax. That means that you can't use the traditional marking of a translateable string (and it's not just tradition; there is a lot of external software that expects it) in that scope.
So it's practically important, if not theoretically necessary, that 'case _' not bind '_'.
Steve
I wasn't imply local to the match statement, but if the match is used inside a function, where using the binding operatior = will create a local name, even if there is a corresponding global name that matches (unless you use the global statement), will a match statement that binds to a name that hasn't bee made a local name by having an explicit assignment to it, actually bind to a global that might be present, or will it create a local? My first feeling is that binding to the global would be surprising.
i.e.
foo = 1
def bar(baz):
match baz:
case 1: print('baz was one')
case foo: print('baz was ', foo)
bar(2)
print(foo)
will this script create a new foo name inside bar, so that when we return, the module global foo is still 1, or did be bind to the global and change it?
Rebinding a global without a global statement would be unexpected (normally we can mutate the global, but not rebind it)
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I think that global binding make no sense, it will break a lot of code silently, think about this def bar(baz): match baz: case bar: pass IMHO, the most obvious solution is that the bind should be available only inside case block and if you need to change a global or a nonlocal you do this explicitly inside the case block, if this is the case you can pickup a bind name that doesn't shadow the desired variable. This way the intention to overwrite a global/nonlocal is clear in code -- “If you're going to try, go all the way. Otherwise, don't even start. ..." Charles Bukowski