[Python-Dev] PEP 292, Simpler String Substitutions

[Guido van Rossum]

> Using compile-time parsing, as in PEP 215, has the advantage that it
> avoids any possible security problems;

It is also the only way to properly support nested scopes.  It would
be confusing and inconsistent if you can use a variable from a nested
scope in an expression but not in a "string display" (which I think is
a cute name for strings with embedded expressions).

> but it also eliminates the possibility of using this for
> internationalization.  I see this as the key tension in the string
> interpolation issue (aside from all the syntax stuff -- which is
> naturally controversial).

Yes, I believe that Barry's main purpose is i18n.  But I think i18n
should not be approached in a cavalier way.  If you need i18n of your
application, you have to be very disciplined anyway.  I think
collecting the variable available for interpolation in a dict and
passing them explicitly to an interpolation function is the way to go
here.

Also, in i18n the interpolation syntax must be usable for translators
who are not necessarily programmers.  I believe the $ notation with
only simple variables is entirely adequate for that purpose -- and
Barry can implement it in a few lines.  (We just adopted this for
Zope3, and while there are all sorts of open issues, $ interpolation
is not one of them.)

--Guido van Rossum (home page: http://www.python.org/~guido/)