[Python-Dev] PEP 383 and GUI libraries

[Cameron Simpson]

On 01May2009 18:38, Martin v. L?wis <martin at v.loewis.de> wrote:
| > Okay, I am wrong about this.  Having a flag to remember whether I had to
| > fall back to the utf-8b trick is one method to implement my requirement,
| > but my actual requirement is this:
| > 
| > Requirement: either the unicode string or the bytes are faithfully
| > transmitted from one system to another.
| 
| I don't understand this requirement very well, in particular not
| the "faithfully" part.
| 
| > That is: if you read a filename from the filesystem, and transmit that
| > filename to another system and use it, then there are two cases:
| 
| What do you mean by "use it"? Things like opening files? How does
| that work? In general, a file name valid on one system is invalid
| on a different system - or, at least, refers to a different file
| over there. This is independent of encodings.

I think he's doing a file transfer of some kind and needs to preserve
the names. Or I would guess the two systems are not both UNIX or there
is some subtlety not yet mentioned, or he'd just use tar or some other
byte-level UNIX tool.

| > Requirement 1: the byte string was valid in the encoding of source
| > system, in which case the unicode name is faithfully transmitted
| > (i.e. the bytes that finally land on the target system are the result of
| > sourcebytes.decode(source_sys_encoding).encode(target_sys_encoding).
| 
| In all your descriptions, I'm puzzled as to where exactly you get
| the source bytes from. If you use the PEP 383 interfaces, you will
| start with character strings, not byte strings, always.

But if both system do present POSIX layers, it's bytes underneath and
the system tools will natively use bytes. He wants to ensure that he can
read using python, using listdir, and elsewhere when he writing using
python, preserve the bytes layer. I think.

In fact it sounds like he may be translating valid unicode and carefully not
altering byte names that don't decode. That in turn implies that the codec
may be different on the two systems.

| > Okay, I find it surprisingly easy to make subtle errors in this encoding
| > stuff, so please let me know if you spot one.  Is it true that
| > srcbytes.encode(srcencoding, 'python-escape').decode('utf-8',
| > 'python-escape') will always produce srcbytes ? 
| 
| I think you mixed up bytes and unicode here: if srcbytes is indeed
| a bytes object, then you can't apply .encode to it.

I think he has encode/decode swapped (I did too back in the uber-thread;
if your mapping is one-to-one the distinction is almost arbitrary).

However, his assertion/hope is true only if srcencoding == 'utf-8'.
The PEP itself says that it works if the decode and encode use the same
mapping.
-- 
Cameron Simpson <cs at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

"How do you know I'm Mad?" asked Alice.
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