[Python-Dev] #2651 - KeyError does not round trip strings

[Fred Drake]

2010/8/4 Łukasz Langa <lukasz at langa.pl>:
> 1. The patch makes KeyError behave analogically to IOError so that the first
> arg is now a message and the second is the actual key.

I agree with Antoine; there's no point to this.

> 2. Some people suggest adding e.key to KeyError. I like the idea but in my
> opinion currently it is not implementable in a reliable way.

This is interesting and useful.

I'd be really happy to see e.key be present if the key is known
(because it was specifically provided to the constructor:
KeyError(key=...)), or not present if the key isn't known.  (The idea
is much less interesting if code can't distinguish between the
key-is-known and the key-not-known cases.)

The runtime and standard library should be adjusted to provide the key
whenever possible, of course.

Though I doubt this would break anything, we've lived without this
long enough that the it doesn't represent a sufficient failing that
the moratorium should be broken.  It can wait.


  -Fred

--
Fred L. Drake, Jr.    <fdrake at gmail.com>
"A storm broke loose in my mind."  --Albert Einstein