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[Python-ideas] String Format Callable Flag (Was: Efficient Debug Logging)
Eric V. Smitheric at trueblade.com
Sun Feb 19 11:21:07 EST 2017
On 2/19/2017 4:23 AM, Pavol Lisy wrote:> On 2/19/17, Eric V. Smith <eric at trueblade.com> wrote:>> On 2/18/2017 2:25 AM, Steven D'Aprano wrote:>>>> I see three problems:>>>>>> (1) It will be a bug magnet. People will accidently write>>>>>> logging.debug('%03d %C03d', 1, expensive())>>>>>>>>> and then not only will their code still be slow, but they'll have to>>> debug mysterious>>>>>> TypeError: 'int' object is not callable>>>>>> exceptions, but only *sometimes*. Most insideously, these Heisenbugs>>> will only occur when they turn the log level all the way up to>>> debugging, which will crash their program *before* logging the error!>>>> I think this is lessened with my proposal to use !c, but it's definitely>> still an issue. Test your logging!>> 1. I think that error message could be understandable at least as this:> '{:g}'.format('a')> ValueError: Unknown format code 'g' for object of type 'str'>> with something like isinstance(arg, callable)Sure, there would be a reasonable error message. The concern (as with logging anything), is that the error case logging is typically poorly tested.> 2. Static checker could check bracket presence if there is !c format> specifier and fire warning.But it's valid to have a function that returns a callable, so these could be false positives. But linters can do whatever they want, I guess.> 3. There could be another problem if return type is callable too...I don't think that's a problem. You'd just print the callable, as you can do today: >>> def fn(): pass... >>> format(fn, '')'<function fn at 0xffee6108>'
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