[Python-Dev] PEP-498: Literal String Formatting

Barry Warsaw barry at python.org
Mon Aug 10 20:31:27 CEST 2015

On Aug 11, 2015, at 03:26 AM, Steven D'Aprano wrote:

>I think I would be happy with f-strings, or perhaps i-strings if we use
>Nick's ideas about internationalisation, and limit what they can evaluate to
>name lookups, attribute lookups, and indexing, just like format().

I still think you really only need name lookups, especially for an i18n
context.  Anything else is just overkill, YAGNI, potentially error prone, or
perhaps even harmful.

Remember that the translated strings usually come from only moderately (if at
all) trusted and verified sources, so it's entirely possible that a malicious
translator could sneak in an exploit, especially if you're evaluating
arbitrary expressions.  If you're only doing name substitutions, then the
worst that can happen is an information leak, which is bad, but won't
compromise the integrity of say a server using the translation.

Even if the source strings avoid the use of expressions, if the feature is
available, a translator could still sneak something in.  That pretty much
makes it a non-starter for i18n, IMHO.

Besides, any expression you have to calculate can go in a local that will get
interpolated.  The same goes for any !r or other formatting modifiers.  In an
i18n context, you want to stick to the simplest possible substitution


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