[Python-Dev] [Python-checkins] cpython: Close #17828: better handling of codec errors (original) (raw)

Walter Dörwald walter at livinglogic.de
Thu Nov 14 18:27:37 CET 2013

On 14.11.13 14:22, Walter Dörwald wrote:

On 13.11.13 17:25, Nick Coghlan wrote:

[...] 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("uucodec") Traceback (most recent call last): File "", line 1, in : decoding with 'uucodec' 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.

http://bugs.python.org/19585 is a patch that implements that. With the patch the following code:

import traceback

@traceback.annotate("while handling x={x!r}")
def handle(x):
   raise ValueError(42)

handle("spam")

will give the traceback:

Traceback (most recent call last):
  File "spam.py", line 8, in <module>
    handle("spam")
  File "frame-annotation/Lib/traceback.py", line 322, in wrapped
    f(*args, **kwargs)
  File "spam.py", line 5, in handle: while handling x='spam'
    raise ValueError(42)
ValueError: 42

Unfortunaty the frame from the decorator shows up in the traceback.

Servus, Walter

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