On 13.11.13 17:25, Nick Coghlan wrote:
On 14 November 2013 02:12, Nick Coghlan <ncogh...@gmail.com> wrote:
On 14 November 2013 00:30, Walter Dörwald <wal...@livinglogic.de> wrote:
On 13.11.13 14:51, nick.coghlan wrote:
http://hg.python.org/cpython/rev/854a2cea31b9
changeset: 87084:854a2cea31b9
user: Nick Coghlan <ncogh...@gmail.com>
date: Wed Nov 13 23:49:21 2013 +1000
summary:
Close #17828: better handling of codec errors
- output type errors now redirect users to the type-neutral
convenience functions in the codecs module
- stateless errors that occur during encoding and decoding
will now be automatically wrapped in exceptions that give
the name of the codec involved
Wouldn't it be better to add an annotation API to the exceptions classes?
This would allow to annotate all exceptions without having to replace the
exception object.
Hmm, it might be better to have the traceback machinery print the
annotation information instead of BaseException.__str__, so we don't get
any compatibility issues with custom __str__ implementations.
There's a reason the C API for this is private - it's a band aid fix,
because solving it properly is hard :)
Note that the specific problem with just annotating the exception
rather than a specific frame is that you lose the stack context for
where the annotation occurred. The current chaining workaround doesn't
just change the exception message, it also breaks the stack into two
pieces (inside and outside the codec) that get displayed separately.
Mostly though, it boils down to the fact that I'm far more comfortable
changing codec exception stack trace details in some cases than I am
proposing a new API for all exceptions this close to the Python 3.4
feature freeze.
Sure, this is something that might go into 3.5, but not 3.4.
A more elegant (and comprehensive) solution as a PEP for 3.5 would
certainly be a nice thing to have, but I think this is still much
better than the 3.3 status quo.
Thinking further about this, I like your "frame annotation" suggestion
Tracebacks could then look like this:
>>> b"hello".decode("uu_codec")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>: decoding with 'uu_codec' codec
failed
ValueError: Missing "begin" line in input data
In fact the traceback already lays out the chain of events. What is
missing is simply a little additional information.
Could frame annotation be added via decorators, i.e. something like this:
@annotate("while doing something with {param}")
def func(param):
do something
annotate() would catch the exception, call .format() on the annotation
string with the local variables of the frame as keyword arguments,
attach the result to a special attribute of the frame and reraise the
exception.
The traceback machinery would simply have to print this additional
attribute.
Servus,
Walter
Servus,
Walter
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