[Python-Dev] Adding a conditional expression in Py3.0

Tue Sep 20 21:00:41 CEST 2005

"Guido van Rossum" <guido at python.org> wrote in message 
news:ca471dc2050920090461aec3da at mail.gmail.com...
> In fact, I think Raymond's example is more properly considered an
> argument for adding a conditional expression than for removing the
> current behavior of the and/or shortcut operators; had we had a
> conditional expression, he wouldn't have tried to use the "x and y or
> z" syntax that bit him.

I agree.
> Given this realization, I'm now -1 on Raymond's idea,

There are a lot of people who use 'or', especially, as intended.
> 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.
"The original version of this PEP proposed the following syntax:
 <expression1> if <condition> else <expression2>
 The out-of-order arrangement was found to be too uncomfortable
 for many of participants in the discussion; especially when
 <expression1> is long, it's easy to miss the conditional while
 skimming."
Your final 'favorite' was apparently (at the top)
"Proposal
 The proposed syntax is as follows:
 (if <condition>: <expression1> else: <expression2>) " (+ 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:
 <condition> ? <expression1> : <expression2>
 2. Adopt a ternary operator built using new or existing keywords.
 The leading examples are:
 <condition> then <expression1> else <expression2>
 (if <condition>: <expression1> else: <expression2>)
 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.
*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.
Terry J. Reedy
> -- 
> --Guido van Rossum (home page: http://www.python.org/~guido/)
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