On Oct 1, 2009, at 5:54 PM, Nick Coghlan wrote:
I believe classes like fmt_braces/fmt_dollar/fmt_percent will be part of a solution, but they aren't a complete solution on their own. (Naming the three major string formatting techniques by the key symbols involved is a really good idea though)
1. It's easy to inadvertently convert them back to normal strings. If a formatting API even calls "str" on the format string then we end up with a problem (and switching to containment instead of inheritance doesn't really help, since all objects implement __str__).
Using containment instead of inheritance makes sure none of the *other* operations people do on strings will appear to work, at least (substring, contains, etc). I bet explicitly calling str() on a format string is even more rare than attempting to do those things.
2. They don't help with APIs that expect a percent-formatted string and do more with it than just pass it to str.__mod__ (e.g. inspecting it for particular values such as '%(asctime)s')
True, but I don't think there's many such cases in the first place, and such places can be fixed to not do that as they're found. Until they are fixed, fmt_braces will loudly fail when used with that API (assuming fmt_braces is not a subclass of str). James