On 14 October 2016 at 14:46, Franklin? Lee <leewangzhong+pyt...@gmail.com> wrote:
> On Oct 14, 2016 9:14 AM, "Gustavo Carneiro" <gjcarne...@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. > > That function is for a different purpose. It selects the first non-null > value from a flat collection. The coalesce operators are for traveling down > a reference tree, and shortcutting out without an exception if the path > ends. > > For example: > return x?.a?.b?.c > >From what I can read in the PEP, it attacks 3 different problems at once: 1. The " null -coalescing" operator is a binary operator that returns its > left operand if it is not null . Otherwise it returns its right operand. > 2. The " null -aware member access" operator accesses an instance member > only if that instance is non- null . Otherwise it returns null . (This is > also called a "safe navigation" operator.) > 3. The " null -aware index access" operator accesses an element of a > collection only if that collection is non- null . Otherwise it returns null > . (This is another type of "safe navigation" operator.) I am proposing a coalesce() function as alternative for (solely) problem 1, while you are talking about problem 2. I do believe problems 2 and 3 are interesting too, and of course coalesce() does not work for them, they do need their own operators. Sorry, I was a bit confused by the PEP attacking 3 (related) problems at once. Thanks. -- Gustavo J. A. M. Carneiro Gambit Research "The universe is always one step beyond logic." -- Frank Herbert
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