[Python-ideas] Binary f-strings

[Nick Coghlan]

On 4 October 2015 at 08:25, Andrew Barnert <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.

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.

I'm not sold on the idea of a struct.pack conversion specifier - if we
added binary format strings, I think it would be better to start with
explicit "pack(value, format)" expressions, and see how that goes for
a release.

Cheers,
Nick.

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