[Python-Dev] Dict suppressing exceptions (original) (raw)

Michael Chermside mcherm at mcherm.com
Thu Aug 10 22:35:14 CEST 2006

Michael Urman writes:

I strongly believe that unicode vs str here is the symptom and not the actual problem. The comparison between two non-us-ascii str/unicode instances is but one of many ways to raise an exception during comparison. [... example ...] Yes this is made up code. But I'm not arguing for a feature; I'm arguing for backwards compatibility. Because we do not know where these legitimate uses are, we cannot evaluate their likelihood to exist nor the level of breakage they will cause. If we make this a warning for any exception, we can satisfy both imagined camps. Those in Armin's position can make that warning raise an exception while debugging, and those using it on purpose can squash it.

See also my example from the beginning of this thread (http://mail.python.org/pipermail/python-dev/2006-August/067978.html). The example wasn't from real code, but it WAS quite plausible -- straightforward use of a popular Python Cookbook recipe.

But we seem to have reached a rough consensus:

Later, Guido writes:

How about we change unicode-vs-str eq to issue a warning (and return False) instead of raising UnicodeException? [... Marc-Andre Lemburg agrees ...] Great! Now we need someone to volunteer to write a patch (which should include doc and NEWS updates) in time for beta 3 (Aug 18).

I don't strongly object to this consensus, but if you haven't glanced at my original example, take a look - it might convince you. The proposed solution will not help with my example. I'm not sure the motivation for breaking code like that example -- the bug-hunting motivation is satisfied by issuing a warning as Michael Urman proposes, then use an exception after one more release when people have had time to fix their code.

-- Michael Chermside

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