[Python-ideas] Binary f-strings

[Eric V. Smith]

On 10/07/2015 01:58 PM, Guido van Rossum wrote:
> Of course that would still leave the door open for struct.pack support
> (maybe recognized by having the string start with <,=, > or @). Pro:
> everybody who currently uses struct.pack will love it. Con: the
> struct.pack mini-language is pretty inscrutable if you don't already
> know it. (And no, I don't propose to invent a different mini-language --
> it's just easier to figure out where to find docs for this when the code
> explicitly imports the struct module.)

Right. I think Steve Dower's idea of :p switching to struct.pack mode is
reasonable. But as Nick says, we don't need to add it on day 1.

Eric.

> 
> On Wed, Oct 7, 2015 at 10:53 AM, Eric V. Smith <eric at trueblade.com
> <mailto:eric at trueblade.com>> wrote:
> 
>     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>
>     > <mailto: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>
>     >     <mailto: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>
>     <mailto: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>
>     <http://python.org/~guido>)
>     >
>     >
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> 
> 
> 
> 
> -- 
> --Guido van Rossum (python.org/~guido <http://python.org/~guido>)