Ethan Furman <[email protected]> added the comment:
> 1. Any syntax change requires a PEP (and, IMO, any such PEP for this issue
> should get rejected: I don't consider this an important enough feature to
> deserve dedicated syntax. Others disagree, which is one of the reasons why a
> PEP is needed. The other, more important, reason is to ensure the new syntax
> is spec'ed out clearly and incorporated into the language reference for the
> benefit of other implementations in the event that it *does* get approved)
I'm not sure why this would be a syntax change. We can already do
try:
1/0
except ZeroDivisionError:
raise ValueError() from MathError()
to explicitly set the __cause__ and ignore the previous context. The
only difference would allowing 'None' to mean 'no cause, discard
previous context'.
> 2. A change that *doesn't* need a PEP is to just adjust the implicit
> exception chaining such that __context__ doesn't get set automatically if it
> has already been set explicitly (it turns out handling this situation was an
> open question in PEP 3134, not a specificied behaviour). That way, this task
> can be handled using a utility function:
>
> def no_context(new_exc):
> new_exc.__context__ = None
> return new_exc
>
> def doXY ():
> # ...
> try:
> page = urlopen( someRequest )
> except urllib.error.URLError as e:
> raise no_context(MyError( 'while doing XY', e ))
This seems like a lot more work than just allowing None to mean none.
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<http://bugs.python.org/issue6210>
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