[Python-ideas] Briefer string format
steve at pearwood.info
Mon Aug 3 16:08:52 CEST 2015
On Sun, Aug 02, 2015 at 10:43:03PM -0400, Eric V. Smith wrote:
> On 8/2/2015 7:46 PM, Mike Miller wrote:
> > Hi,
> > I don't understand how we got to arbitrary expressions.
> I think here:
> > There was probably an edge case or two, but I wasn't expecting
> > str(eval(s)) to be the answer, and one I'm not sure I'd want.
> As I pointed out earlier, it's not exactly str(eval(s)). Also, what's
> your concern with the suggested approach? There are no security concerns
> as there would be with eval-ing arbitrary strings.
Language features should be no more powerful than they need to be. It
isn't just *security* that we should be concerned about, its also about
readability, learnability, the likelihood of abuse by writing
unmaintainable Perlish one-liners, and the general increase in
Or to put it another way... YAGNI.
We started of with a fairly simple and straightforward feature request:
to make it easy to substitute named variables in format strings. We
ought to be somewhat cautious about accepting even that limited version.
After all, hundreds of languages don't have such a feature, and Python
worked perfectly well without it for over 20 years. This doesn't add
anything to the language that cannot already be done with % and
But suddenly we've gone from a feature request that has been routinely
denied many times in the past (having variables be automatically
substituted into strings), to full-blown evaluation of arbitrarily
complex expressions being discussed as if it were a done-deal.
I've heard of the trick of asking for a pony if you actually want a
puppy, but this is the first time I've seen somebody ask for a puppy and
be given a thoroughbred.
Anyway, there's no harm done, since this is going through the PEP
process. It just strikes me as so unlike the usual conservatism,
particularly when it comes to syntax changes, that it surprised me.
Perhaps somebody slipped something in the water? :-)
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