[Python-Dev] cpython (3.2): Issue #14123: Explicitly mention that old style % string formatting has caveats (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Sun Feb 26 22:13:11 CET 2012

On Mon, Feb 27, 2012 at 5:23 AM, Eli Bendersky <eliben at gmail.com> wrote:

It would be nice to call it something else than "printf-style formatting". While it is certainly modelled on printf(), knowledge of C or printf is not required to understand %-style formatting, nor even to appreciate it. +1. The section is already titled "old string formatting operations" so if this name is acceptable it should be reused. If it's not, it should then be consistently changed everywhere.

I deliberately chose printf-style as being value neutral (whereas old-style vs new-style carries a heavier recommendation that you should be using the new one). Sure you don't need to know printf to understand it, but it needs some kind of name, and "printf-style" acknowledges its roots. Another value-neutral term is "mod-style", which describes how it is invoked (and I believe we do use that in a few places already).

I didn't actually expect that paragraph to be incorporated wholesale into the docs - it was intended as a discussion starter, not a finished product. Aside from the last two sentences, the other big problem with it is that print-style formatting does support formatting arbitrary objects, they're just forced to go through type coercions whereas .format() allows objects to define their own formatting specifiers (such as datetime with strftime strings).

Cheers, Nick.

-- Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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