On 2014-01-07 17:46, Andrew Barnert wrote:
I think Stephen's name 7-bit is confusing people. If you try to
interpret the name sensibly, you get Steven's broken interpretation.
But if you read it as a nonsense word and work through the logic, it
all makes sense.
On Jan 7, 2014, at 7:44, Steven D'Aprano st...@pearwood.info wrote:
I was thinking about Ethan's suggestion of introducing a new bytestring
class and a lot of these suggestions are what I thought the bytestring
class could do.
[snip]
Suppose we take a pure-ASCII byte-string and decode it:
b'abcd'.decode('ascii-compatible')
That would be:
bytestring(b'abcd')
or even:
bytestring('abcd')
[snip]
Suppose we take a byte-string with a non-ASCII byte:
b'abc\xFF'.decode('ascii-compatible')
That would be:
bytestring(b'abc\xFF')
Bytes outside the ASCII range would be mapped to Unicode low
surrogates:
bytestring(b'abc\xFF') == bytestring('abc\uDCFF')
[snip]
Presumably they will compare equal, yes?
I would hope not. One of them has the Unicode character U+FF, the
other has smuggled byte 0xFF, so they'd better not compare equal.
However, the latter should compare equal to 'abc\uDCFF'. That's the
entire key here: the new representation is nothing but a more compact
way to represent strings that contain nothing but ASCII and surrogate
escapes.
[snip]
A concrete example:
s = b'abcd'.decode('ascii-compatible')
t = 'x' # ASCII-compatible
s + t
= returns 'abcdx', with the 7-bit repr flag cleared.
s = bytestring(b'abcd')
t = 'x' # ASCII-compatible
s + t
= returns 'abcdx'
Right. Here both s and t are normal 8-bit strings reprs in the first
place, so the new logic doesn't even get invoked. So yes, that's what
it returns.
s = b'abcd'.decode('ascii-compatible')
t = 'ÿ' # U+00FF, non-ASCII.
s + t
= returns 'abcd\uDCFF', with the 7-bit repr flag set
s = bytestring(b'abcd')
t = 'ÿ' # U+00FF, non-ASCII.
s + t
= returns 'abcd\xFF'
[snip]
There were also some other equivalences I was considering:
bytestring(b'abc') == b'abc'
bytestring(b'abc') == 'abc'
The problem there is that it wouldn't be transitive because:
b'abc' != 'abc'
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