Curious assignment behaviour
phr-n2001d at nightsong.com
Wed Oct 10 09:29:19 CEST 2001
"Tim Peters" <tim.one at home.com> writes:
> [Paul Rubin, on an expression assignment operator]
> > Why on earth does it have to be different from the statement assignment
> > operator? What's wrong with
> > while x=get_next(): whatever(x)
> > I just don't buy the rationale that using = instead of == is a big source
> > of bugs. In 25 years of hacking C code, I think I've seen that error
> > maybe once or twice.
> I suggest you're highly atypical here, Paul. This was the very first of the
> gotchas listed in Andrew Koenig's classic (late 80s) "C Traps and Pitfalls",
> and has made nearly every list of C "deadly sins" I've seen since then.
> I've wasted weeks of my own life helping people track this error down in C,
> too often under extreme time or customer pressure. The experience of the
> other folks at PythonLabs is similar, so even if it's a disease you're
> immune to, you can be sure this will never go in.
The thing is, it's just not a matter of MY immunities. I've spent
plenty of time debugging other people's code too, and have encountered
all kinds of errors in both their code and mine. The =/== mistake has
just been very rare in my experience. Can it be that the Unix
compilers I use flag the error a lot of the time, so it gets fixed
quickly, while Windows compilers don't flag it, and you're mostly
using Windows compilers?
Anyway, I can live with "while x:=get_next()" instead of x=get_next.
But I feel seriously cramped in Python when I have to say
if not x: break
so I hope something is done about the issue.
> Oops! The assert turned out to be the perversely self-fulfilling:
> assert(i = 1);
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