[Python-ideas] PEP 505 -- None-aware operators

[Gustavo Carneiro]

On 14 October 2016 at 14:19, אלעזר <elazarg at gmail.com> wrote:

> On Fri, Oct 14, 2016 at 4:14 PM Gustavo Carneiro <gjcarneiro at gmail.com>
> wrote:
>
>> Sorry if I missed the boat, but only just now saw this PEP.
>>
>> Glancing through the PEP, I don't see mentioned anywhere the SQL
>> alternative of having a coalesce() function: https://www.
>> postgresql.org/docs/9.6/static/functions-conditional.
>> html#FUNCTIONS-COALESCE-NVL-IFNULL
>>
>> In Python, something like this:
>>
>> def coalesce(*args):
>>     for arg in args:
>>         if arg is not None:
>>              return arg
>>     return None
>>
>> Just drop it into builtins, and voila.   No need for lengthy discussions
>> about which operator to use because IMHO it needs no operator.
>>
>> Sure, it's not as sexy as a fancy new operator, nor as headline grabbing,
>> but it is pretty useful.
>>
>>
> This has the downside of not being short-circuit - arguments to the
> function are evaluated eagerly.
>

I see.  short-circuiting is nice to have, sure.

But even without it, it's still useful IMHO.  If you are worried about not
evaluating an argument, then you can just do a normal if statement instead,
for the rare cases where this is important:

result = arg1
if result is None:
   result = compute_something()

At the very least I would suggest mentioning a simple coalesce() function
in the alternatives section of the PEP.

coalesce function:
  Pros:
    1. Familiarity, similar to existing function in SQL;
    2. No new operator required;
  Cons:
    1. Doesn't short-circuit the expressions;
    2. Slightly more verbose than an operator;


Thanks.

-- 
Gustavo J. A. M. Carneiro
Gambit Research
"The universe is always one step beyond logic." -- Frank Herbert
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