Barry Warsaw wrote:
raise e from ...
is certainly cute, but not very informative. Triple-dots will be confusing
and difficult to read in documentation and code, and Ellipsis has no logical
connection to the purpose of this PEP. So while I'm +1 on everything else in
the PEP, I'm -1 on this particular decision.
One of the alternatives states:
Create a special exception class, __NoException__.
Rejected as possibly confusing, possibly being mistakenly raised by users,
and not being a truly unique value as None, True, and False are.
I think this should be revisited. First, `__NoException__` doesn't need to be
an exception class. Ellipsis isn't so this doesn't need to be either. I have
no problem adding a new non-exception derived singleton to mark this. And
while __NoException__ may be a little confusing, something like __NoCause__
reads great and can't be mistaken for a raiseable exception.
The problem I have with names like __NoException__, __NoCause__,
__NoWhatever__ is that is sounds a lot like None -- in otherwords, like
there won't be any chaining.
So your example would then be:
try:
try:
raise IndexError()
except:
raise CustomError() from None
except CustomError as e:
# nevermind, let's see the whole thing after all
raise e from __NoCause__
If we do switch from Ellipsis to something else I think a name like
__Chain__ would be more appropriate. Or __ExcChain__.
raise e from __ExcChain__
Less cute, but probably less confusing.
~Ethan~
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