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

[Steven D'Aprano]

On Tue, Jul 24, 2018 at 08:07:36AM -0400, Richard Damon wrote:

> The fact that you changed NullCoalesce into Foo to show lack of 
> explicitness seems a straw-man.

I understood Rhodri as making the point that if you don't know what 
NullCoalesce means or does, it might as well be called Foo. There's no 
hint in the syntax that something magical is happening:


    MyClass(obj).spam.eggs  # ordinary attribute lookup

    YourClass(obj).spam.eggs  # still ordinary attribute lookup

    Mxyzptlk(obj).spam.eggs  # looks like ordinary attribute lookup

    NullCoalesce(obj).spam.eggs  # IT'S A TRAP!



> Words are FULL of meaning, while symbols are less so.

It isn't a competition to squeeze as much meaning as possible into a 
single word or symbol. Precision is more important than fullness.

A case in point: the word "add" has six meanings listed by WordNet, and 
the Mobi Thesaurus gives 102 synonyms for it. A function or method called "add" 
could do anything:

- add users to a database;
- add pages to a chapter;
- add elements to a set;
- add items to a queue;

etc. In contrast, the + symbol in Python has two standard meanings:

- numeric addition;
- sequence concatenation;

and while it is true that with operator overloading a class could make 
the + operator do anything, that is usually taken as an argument to 
avoid operator overloading, or at least use it cautiously.

Surely you don't think that the + operator is a mistake because the word 
"add" is more full of meaning than the symbol? If not, what point were 
you trying to make?


> The biggest issue I see with the use of ? here is 
> that ? does have some meaning, it says we are going to be (or have) 
> asked a question, it doesn’t tell us what the question is.

Sometimes you just have to learn the meanings of words or symbols.

What does NullCoalesce mean? Until this PEP was proposed, I had no idea 
this was even a thing, and in truth I actually had to look up "coalesce" 
in a dictionary to be sure I understood it correctly, because the 
context doesn't seem quite right.

(It still doesn't -- it might be the standard comp sci term for this 
feature, but I don't think it quite matches the ordinary usage of the 
word.)

Ask a dozen programming beginners what "NullCoalesce" does, and I expect 
every one of them will say "No idea".

Strangely enough, nobody complains about having to learn what "import" 
does, or slicing syntax x[:], or string backslash escapes "\n", or 
"property". Because we're used to them, we just accept that you have to 
learn the meaning of things the first time you see them. We aren't born 
knowing what "class" does, or the difference between x[a] and x(a).

Every single one of us, without exception, had to learn what . means at 
some point or another.

And yet, its wailing and gnashing of teeth and panic in the streets over 
the idea that people might have to learn what ?. means in the same way 
they learned what **kwargs or mylist[1:] or obj.attr means.

    "It's a question, but what is the question? How will I ever
    find out? If only there was a website where I might look up
    Python operators and learn what they do!!!"


> ?. has some indication that we are doing an attribute access that is 
> in some way conditional, but a?.b could mean that we are conditional 
> on a not being null, or it could be asking to suppress any and all 
> error in getting b, even if a is an int and thus doesn’t have a b. The 
> words carry a lot more meaning.

Yeah, because words are always obvious.

import ast  # Who can remember all these damned TLAs?
import bdm  # Births Deaths Marriages?
import csv  # Court Services Victoria?
import mailcap  # what the postman wears on his head?
import pickle  # something to do with condiments?
import turtle  # somebody is taking the micky
import curses  # good thing I'm not superstitious


    "But Steve, you don't understand. Having to learn the meaning
     of words you haven't learned before is right and proper and
     unavoidable. But all new punctuation symbols must be intuitively
     obvious to newborn babies, or else they are the Devil's Mark,
     or Perl, not sure which is worse."

(Its called sarcasm, not "strawman". Just sayin'.)


-- 
Steve