[Python-Dev] Adding a conditional expression in Py3.0 (original) (raw)

Guido van Rossum guido at python.org
Tue Sep 20 21:17:41 CEST 2005

On 9/20/05, Terry Reedy <tjreedy at udel.edu> wrote:

"Guido van Rossum" <guido at python.org> wrote in message > and +1 on adding a conditional expression. I believe (y if x else z) > was my favorite last time, wasn't it?

No. That was your original proposal, which you later rejected.

Thanks for setting me straight; upon re-reading the PEP I couldn't even remember which one I favored at the time!

Your final 'favorite' was apparently (at the top)

"Proposal The proposed syntax is as follows: (if : else: ) " (+ elif parts) selected from "Summary of the Current State of the Discussion Groups are falling into one of three camps: 1. Adopt a ternary operator built using punctuation characters: ? : 2. Adopt a ternary operator built using new or existing keywords. The leading examples are: then else (if : else: ) 3. Do nothing." Given the later addition of generator expressions with mandatory parentheses , the mandatory-parentheses version of a conditional expression looks less strange to me than it did then ;-). So I could happily use it even though I may still lean toward the other option 2 version (then-else) due to its not needing ':'s or a third elseif term for chaining.

I think I'd prefer (if then else ) i.e. no colons. None of the other expression forms (list comprehensions and generator expressions) involving statement keywords use colons.

If you want general community input, I would suggest a runoff ballot with those four choices (and a summary of pros and cons of each), or fewer if you see any as unacceptible.

If there's one thing I've learned from the PEP 308 vote, it is that votes for language don't work. I prefer some discussion on Python-dev after which I pick one.

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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