On 1/14/2014 4:46 AM, Nick Coghlan wrote:
The one remaining way I could potentially see a formatb method working
is along the lines of what Glenn (I think) suggested: just like struct
definitions, the formatb specifier would have to consist*solely* of
substitution fields. However, that's getting awfully close to being
just an alternate spelling for the struct module or bytes.join at that
point, which hardly makes for a compelling case to add two new methods
to a builtin type.
Yes, after someone drew the parallel between my "format specifier only"
pedantry, and struct.pack (which I hadn't used), I agree that they are
almost just different spellings for the same things.
The two differences I could see is that struct.pack doesn't support
variable length items, and struct.pack doesn't support "interpolation",
which is the whole beauty of the % type syntax... the ability to have a
template, and interpolate values.
My pedantry DID allow for template work, but they had to be specified in
HEX the way I specified it yesterday.
Let me repeat that syntax:
b"%{hex-codes}v"
That was mostly so the format string could be ASCII, yet represent any
byte. That is somewhat clunky, when actually wanting to represent
characters. At the next level of abstraction, one could define a
"format builder" that would take Unicode specifications, and "compile"
them into the binary interpolation strings, but if doing that, you could
just as well compile them into functions using struct.pack formats, with
the parameters interspersed with the "template" data, except for
struct.pack's inability to deal with variable length data.
So struct is attempting to emulate C structs, and variable length data
is extremely awkward in C structs also, so I guess it provides a good
emulation :)
So if I were to look for features to add to Python3 to support template
interpolation for users of non-ASCII encodings, which could, of course,
also be used by users of ASCII-based encodings, I guess I would recommend:
1) extend struct to handle variable length data items
2) provide a sample format compiler function that would translate a
Unicode format description into a function that would use struct.pack,
and pre-encode (according to the format specification) the template
parts into parameters for struct.pack).
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