On Mon, Jan 6, 2014 at 11:57 AM, Stephen J. Turnbull
I'm not missing a new type, but I am missing the format method on the binary types.
I'm curious about precisely what your use cases are, and just what formatting they need.
One use case I came across was when creating chunks for the HTTP chunked encoding. Chunks contain a ascii header, a raw/encoded chunk body, and an ascii trailer. Using a bytes.format, it would look like this: chunk = '{0:X}\r\n{1}\r\n'.format(len(buf), buf) This is what I am using now: chunk = bytearray() chunk.extend('{0:X}\r\n'.format(len(buf)).encode('ascii')) chunk.extend(buf) chunk.extend('\r\n'.encode('ascii')) Regards, Geert
The problem that Python 2 code has over and over imposed on me is that the temptation to avoid the overhead of conversion to and then from unicode when processing text by just using str results in the equivalent of
bs1 = returns_a_bytestring_encoded_in_utf8() bs2 = returns_a_bytestring_encoded_in_koi8()
bs3 = b'{0} {1}'.format(bs1, bs2) # and lose big when something expects valid UTF-8 in bs3
In low-level code, the assignments to bs1, bs2, and bs3 are likely to be in three separate contexts, even three separate modules. I understand about consenting adults, but it's just too hard to enforce good practice here if you make it easy to pass around and operate on encoded bytestrings. I don't see how you avoid this pitfall, except by making it easier to pass around Unicode than encoded strings. And given that encoding and decoding are unavoidable, that means making use of bytestrings with text semantics painful.
So to answer my question from my own point of view, for example, I would have no problem at all with
b'{0:c}'.format(27) == b'\x1b' # insert an ASCII ESC character
I would be leery of
b'{0:s}'.format(b'\x1b[M') == b'\x1b[M' # insert a ANSI control sequence
for the reason given above (for this use case, I would prefer
blue_code = ord('M') # Or b'M', doesn't matter! b'\x1b[{0:c}'.format(blue_code) == b'\x1b[M'
-- and forgive me for not looking up my ANSI color sequences, it's only luck if that's close) and I would consider
b'{0:d}'.format(27) == b'27' # insert the ASCII representation
to be an abomination since there's no reason to suppose that any given bytestring is encoded in an ASCII-compatible way, or bigendian for that matter. Ditto everything else that involves representing a number as a string of numeric characters.