[Python-ideas] In-place assignment for "boolean or"?

[Steven D'Aprano]

On Mon, Mar 26, 2018 at 01:48:34PM +0100, Cammil Taank wrote:
> Hi,
> 
> I find a common idiom in Python is:
> 
> x = x or 'some other value'

I don't find it very common. I don't think I've ever used it or seen it. 
I've occasionally used:

    spam = eggs or 'something'

but mostly I use:

    result = function(eggs or 'something')

(and even that is quite unusual). But others may use it more often.


> This is highly reminiscent of the problem inplace operators solve.

Not really: the other augmented operators all connect to ordinary 
operators that can be overloaded. But `or` is special, it's a 
short-cutting operator that is treated specially by the interpreter.

And even if x is mutable, there's no way to make this an in-place 
operation. After `x = x or y`, there are only two possibilities:

- x is still a reference to whatever it was before the operation;
- or x now refers to the same object as y.

So this is very different behaviour to (say) += and the other augmented 
operators.

 
> Would it be a good idea to consider an inplace operator for this, perhaps:
> 
> x or= 'some other value'

Mixing a keyword with a symbol like that looks really weird.

Others may disagree, but to me, this pattern isn't common enough to 
justify specialist syntax. I might be a little less negative if the 
syntax didn't look so strange to me.

But only a little.


-- 
Steve