[Python-Dev] Re: PEP 292, Simpler String Substitutions

Christian Tismer tismer@tismer.com
Sun, 23 Jun 2002 04:04:59 +0200

Barry A. Warsaw wrote:
>>>>>>"CT" == Christian Tismer <tismer@tismer.com> writes:
>     CT> If there are program variables directly accessible inside
>     CT> strings to be interpolated, then I see possible abuse, if
>     CT> abusers manage to supply such a string in an unforeseen way.
> For literal strings in .py files, the only way that's going to happen
> is if someone you don't trust is hacking your source code, /or/ if you
> have evil translators sneaking in bogus translation strings.  The
> latter can be solved with a verification step over your message
> catalogs, while the former I leave as an exercise for the reader. :)
> So still, I trust automatic interpolation of program vars for literal
> strings, but for strings coming from some other source (e.g. a web
> form), then yes, you obviously want to be explicit about the
> interpolation dictionary.

 From another reply:
 >     def whereBorn(name):
 > 	country = countryOfOrigin(name)
 > 	return _('$name was born in $country')

Ok, I'm all with it.
Since a couple of hours, I'm riding the following horse:

- $name, $(name), $(any expr)  is just fine
- all of this is compile-time stuff

The idea is:
Resolve the variables at compile time.
Don't provide the feature at runtime.

Here a simple approach. (I'm working on a complicated, too):
(assuming the "e" character triggering expression extraction)

     def whereBorn(name):
	country = countryOfOrigin(name)
	return _(e'$name was born in $country')

is accepted by the grammar, but turned into the
equivalent of:

     def whereBorn(name):
         country = countryOfOrigin(name)
         return _('%(x1)s was born in %(x2)s') % {
           "x1": name, "x2": country}

That is: The $ stuff is extracted, turning the fmt
string into something anonymous. Your _() processes
it, then the variables are formatted in.
This turns the $ stuff completely into syntactic
sugar. Any Python expression inside $() is allowed,
it is compiled as if it were sitting inside the dict.
I also believe it is a good idea to do the _() on
the unexpanded string (as shown), since the submitted
values are most probably hard to translate at all.

cheers - chris

Christian Tismer             :^)   <mailto:tismer@tismer.com>
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