[Python-Dev] #2651 - KeyError does not round trip strings (original) (raw)

Fred Drake fdrake at acm.org
Wed Aug 4 16:23:02 CEST 2010

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.    "A storm broke loose in my mind."  --Albert Einstein

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