Paul Rubin <http://[EMAIL PROTECTED]> wrote:
> [EMAIL PROTECTED] (Alex Martelli) writes: > > If it changed the semantics of for-loops in general, that would be quite > > inconvenient to me -- once in a while I do rely on Python's semantics > > (maintaining the loop control variable after a break; I don't recall if > > I ever used the fact that the variable is also maintained upon normal > > termination). > > Some languages let you say things like: > for (var x = 0; x < 10; x++) > do_something(x); > and that limits the scope of x to the for loop. That seems like a > reasonable way to offer for-loops that don't leak. Yes, that's how C++ introduced it, for example. But note that, after waffling quite a bit in various betas of VC++, Microsoft ended up having this form *not* limit the scope, for years, in two major releases; I'm not privy to their reasons for accepting the syntax but rejecting its key semantic point, and I think they've finally broken with that in the current VC++ (don't know for sure, haven't used MS products for a while). But it sure made for quite a long transition period. It's far from clear to me that it's worth complicating Python by introducing a third form of loop, next to normal while and for ones, to mean "a for loop whose control variables are hyperlocalized" (plural, in general, of course -- ``for n, v in d.iteritems():'' etc). > > (musing...): I think the reason there's no real use case for using a > > listcomp's control variable afterwards is connected to this distinction: > > listcomps have no `break'... > > Of course you can still break out of listcomps: You can abort them by having an exception raised -- that's quite a different issue. > class oops: pass > def f(x): > if x*x % 11 == 3: raise oops > return x*x > try: > lcomp = [f(x) for x in range(10)] > except oops: pass > print x > > prints "5" This way, you don't get anything assigned to lcomp. break is quite different from raise, which aborts the whole caboodle up to the handler. Alex -- http://mail.python.org/mailman/listinfo/python-list
