On 1/13/2014 4:32 PM, Guido van Rossum wrote:
> I will doggedly keep posting to this thread rather than creating more
threads.
Please permit to to doggedly keep pointing you toward the possible
solution I posted on the tracker last October.
But formatb() feels absurd to me. PEP 460 has neither a precise
specification or any actual examples, so I can't tell whether the
Two days ago, I reposted byteformat() here on pydev with a precise text
specification added to the code, and with an expanded test example. I
have just added another example based on your question below.
intention is that the format string can *only* contain {...} sequences
or whether it can also contain "regular" characters. Translating to
formatb(), my question comes down to the legality of the following
example:
b'Hello, {}'.formatb(name) # Where name is some bytes object
If this is allowed, it reintroduces the ASCII bias (since the
substring 'Hello' is clearly ASCII).
Since byteformat() uses re to find {<format-spec>} replacement fields,
it only has such ascii bias as re has, which I believe is not much, if
any. As far as re and byteformat are concerned, everything outside of
the {...} fields is uninterpreted bytes. As far as bytes.join is
concerned, both joiner and joined are uninterpreted bytes.
>>> byteformat(b'\x00{}\x02{}def', (b'\x01', b'abc',))
b'\x00\x01\x02abcdef'
re.split produces [b'\x00', b'', b'\x02', b'', b'def']. The only ascii
bias is the one already present is the representation of bytes, and the
fact that Python code must have an ascii-compatible encoding.
The advantage of
byteformat(b'\x00{}\x02{}def', (b'\x01', b'abc',))
over directly writing
b''.join([b'\x00', b'\x01', b'\x02', b'abc', b'def']
is that one does not have to manually split the presumably constant
template into chunks and interleave them with the presumable variable
chunks.
Here is the example that I used for testing, including non-blank format
specs.
bformat = b"bytes: {}; bytearray: {:}; unicode: {:s}; int: {:5d}; float:
{:7.2f}; end"
objects = (b'abc', bytearray(b'def'), u'ghi', 123, 12.3)
result = byteformat(bformat, objects)
>>>
b'bytes: abc; bytearray: def; unicode: ghi; int: 123; float: 12.30; end'
The additional advantage here is the automatic encoding of formatted
strings to bytes. As posted, byteformat() uses the str.encode defaults
(encoding='utf-8', errors='strict'). But as I said in the post, these
could become parameters to the function that are passed on to str.encode.
The design reuses re.split, bytes.join, format, and the format
specification. By re-using the format-spec as is, the only new thing to
learn is that blank specs correspond to bytes instead of strings. This
is easier to design, implement, and learn than if the format-spec is
limited to disallow some things (after much bike-shedding over what to
eliminate ;-).
I would appreciate your comment on this proposal.
--
Terry Jan Reedy
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
https://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
