I'm coming from Tcl-world ...
Martin v. Löwis
loewis at informatik.hu-berlin.de
Fri Aug 2 16:49:10 CEST 2002
Andreas.Leitgeb at siemens.at (Andreas Leitgeb) writes:
> 1.) A 'for'-loop like in Tcl or in C, where you have separate
> Init-, condition and increment-blocks, that control the loop.
> (Of course, there's while, which can emulate all, but with that,
> getting "continue" straight (that is: jump to the "increment-part"
> of the body) is probably some hassle ...)
I think you'll find that you rarely need those, since you usually
iterate over some sequence. In those cases where you do need this
construct - yes, a while loop is the idiom you'll use.
> 2.) A 'switch'-thing: like a big if-elif-elif-elif-...-else but
> which evaluates its expression only once ... and then does all the
PEP 275 proposes to include such a thing. You are encouraged to
comment on the PEP, either in this group, or by contacting the PEP
> 3.) event-based scripting. (like 'fileevent','after',... in Tcl)
> I've read somewhere, that with tkinter I get access to tcl's event-stuff,
> But I was more after something that also works without Gui and without
> actually using Tcl through Python. Is there a builtin module that
> wraps the select() or poll() systemcall, and invokes the registered
> functions if "their" respective channel becomes readable/writable
> or a timer runs out ?
I think the asyncore module is closest to that - although it is really
common to use select/poll explicitly, or to use threads.
> 4.) "calls by reference": maybe I'm totally misunderstanding pythons
> function-call-concepts. I want to pass a non-global variable to
> a subroutine, have it changed there, and find that variable
> changed in the calling context:
> of course doesn't work out the way I'm looking for. So what's the
> easiest, and (if different) what's the python'iest way to do it ?
The common approach is to mutate mutable objects. E.g.
o.value += 1
p = Counter()
p.value = 0
Of course, for this application, you use proper methods:
self.value = 0
self.value += 1
p = Counter()
> Is this a bug in old versions, or has something severely changed from
> 2.0 to 2.2 that affects performance so much ? Or is this just one of
> many reasons to upgrade to 2.2.1 on all the machines ?-)
I think this might be an improvement in the list.append
implementation: the map() call will add elements one-by-one, which
used to be quadratic, but isn't anymore.
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