[Python-ideas] Binary f-strings

[Eric V. Smith]

On 10/07/2015 12:25 PM, Guido van Rossum wrote:
> I think bf'...' should be compared to b'...' % rather than to f'...'.
> IOW bf'...' is to f'...' as b'...'% is to '...'%.

I'm leaning this way, at least in the sense of "there's a fixed number
of known types supported, and there's no extensible protocol involved.

Eric.

> 
> On Wed, Oct 7, 2015 at 5:34 AM, Andrew Barnert <abarnert at yahoo.com
> <mailto:abarnert at yahoo.com>> wrote:
> 
>     On Oct 7, 2015, at 04:35, Nick Coghlan <ncoghlan at gmail.com
>     <mailto:ncoghlan at gmail.com>> wrote:
>     >
>     >> On 4 October 2015 at 08:25, Andrew Barnert <abarnert at yahoo.com <mailto:abarnert at yahoo.com>> wrote:
>     >> Nick's suggestion of having it do %-formatting makes sense. Yes, it means
>     >> that {count:03} is an error and you need '{count:03d}', which is
>     >> inconsistent with f-strings. But that seems like a much less serious problem
>     >> than bytes formatting not being able to handle bytes.
>     >
>     > Exactly, if someone is mistakenly thinking
>     > bf"{header}{content}{footer}" is equivalent to
>     > f"{header}{content}{footer}".encode(), they're likely to get immediate
>     > noisy errors when they start trying to format fields.
> 
>     Except that multiple people in this thread are saying that'd exactly
>     what it should mean (which I think is a very bad idea).
> 
>     > The parallel I'd attempt to draw is that:
>     >
>     >    f"{header}{content}{footer}" is to "{}{}{}".format(header, content, footer)
>     >
>     > as:
>     >
>     >    bf"{header:b}{content:b}{footer:b}" would be to b"%b%b%b" %
>     > (header, content, footer)
>     >
>     > To make the behaviour clearer in the latter case, it may be reasonable
>     > to *require* an explicit field format code, since that corresponds
>     > more closely to the mandatory field format codes in mod-formatting.
> 
>     Are you suggestive that if a format specifier is given, it must
>     include the format code (which seems perfectly reasonable to
>     me--guessing that :3 means %3b is likely to be wrong more often than
>     it's right…), or that a format specifier must always be given, with
>     no default to :b (which seems more obtrusive and solves less of a
>     problem).
> 
> 
> 
> 
> -- 
> --Guido van Rossum (python.org/~guido <http://python.org/~guido>)
> 
> 
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