[Python-Dev] PEP 293, Codec Error Handling Callbacks

Martin v. Loewis martin@v.loewis.de
12 Aug 2002 17:41:46 +0200

Walter D=F6rwald <walter@livinglogic.de> writes:

>  > - charmap_encoding_error, which insists on implementing known error
>  >   handling algorithms inline,
> This is done for performance reasons.

Is that really worth it? Such errors are rare, and when they occur,
they usually cause an exception as the result of the "strict" error

I'd strongly encourage you to avoid duplication of code, and use
Python whereever possible.

> The PyCodec_XMLCharRefReplaceErrors functionality is
> independent of the rest, so moving this to Python
> won't reduce complexity that much. And it will
> slow down "xmlcharrefreplace" handling for those
> codecs that don't implement it inline.

Sure it will. But how much does that matter in the overall context of
generating HTML/XML?

>  > - the UnicodeError exception methods (which could be omitted, IMO).
> Those methods were implemented so that we can easily
> move to new style exceptions.=20

What are new-style exceptions?

> The exception attributes can then be members of the C struct and the
> accessor functions can be simple macros.

Again, I sense premature optimization.

> 1. For each error handler two Python function objects are created:
> One in the registry and a different one in the codecs module. This
> means that e.g.
> codecs.lookup_error("replace") !=3D codecs.replace_errors

Why would this be a problem?=20

> We can fix that by making the name ob the Python function object
> globally visible or by changing the codecs init function to do a
> lookup and use the result or simply by removing codecs.replace_errors

I recommend to fix this by implementing the registry in Python.

> 4. Assigning to an attribute of an exception object does not
> change the appropriate entry in the args attribute. Is this
> worth changing?

No. Exception objects should be treated as immutable (even if they
aren't). If somebody complains, we can fix it; until then, it suffices
if this is documented.

> 5. UTF-7 decoding does not yet take full advantage of the machinery:
> When an unterminated shift sequence is encountered (e.g. "+xxx")
> the faulty byte sequence has already been emitted.

It would be ok if it works as good as it did in 2.2. UTF-7 is rarely
used; if it is used, it is machine-generated, so there shouldn't be
any errors.