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("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.
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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