On Fri, May 10, 2013 at 4:27 PM, Eli Bendersky <eliben@gmail.com> wrote:
On Fri, May 10, 2013 at 11:48 AM, Guido van Rossum <guido@python.org> wrote:
I just spent a few minutes staring at a bug caused by a missing comma -- I got a mysterious argument count error because instead of foo('a', 'b') I had written foo('a' 'b').
This is a fairly common mistake, and IIRC at Google we even had a lint rule against this (there was also a Python dialect used for some specific purpose where this was explicitly forbidden).
Now, with modern compiler technology, we can (and in fact do) evaluate compile-time string literal concatenation with the '+' operator, so there's really no reason to support 'a' 'b' any more. (The reason was always rather flimsy; I copied it from C but the reason why it's needed there doesn't really apply to Python, as it is mostly useful inside macros.)
Would it be reasonable to start deprecating this and eventually remove it from the language?
I would also be happy to see this error-prone syntax go (was bitten by it a number of times in the past), but I have a practical question here:
Realistically, what does "start deprecating" and "eventually remove" means here? This is a significant backwards-compatibility breaking change that will *definitely* break existing code. So would it be removed just in "Python 4"? Or are you talking about an actual 3.x release like "deprecate in 3.4 and remove in 3.5" ?
It's probably common enough that we'd have to do a silent deprecation in 3.4, a nosy deprecation in 3.5, and then delete it in 3.6, or so. Or maybe even more conservative. Plus we should work on a conversion tool that adds + and () as needed, *and* tell authors of popular lint tools to add rules for this. The hacky proposals for making it a syntax warning "sometimes" don't feel right to me. I do realize that this will break a lot of code, and that's the only reason why we may end up punting on this, possibly until Python 4, or forever. But I don't think the feature is defensible from a language usability POV. It's just about backward compatibility at this point. -- --Guido van Rossum (python.org/~guido)