[Python-ideas] Unpacking iterables for augmented assignment

[Jonathan Fine]

Hi James and Steve

Myself and Steve wrote:

>> Notice that '+=' creates uses the same object when the object is a
>> list, but creates a new object. This raises the question: Why and how
>> does Python behave in this way?

> Lists are mutable and can be modified in place. Tuples are immutable and
> cannot be.

This correctly answers why this happens.

Steve: I wanted James to think about this question. He learns more
that way. (I already knew the answer.)

James: Combining tuple assignment with increment assignment in a
single statement will increase the cognitive burden on both writer and
reader of the line of code.

In other words, in most cases
> a += <EXP1>
> b += <EXP2>
is easy to write and read than
> a, b += <EXP1>, <EXP2>

Now look at:
> a, b += my_object.some_method(args)

It is simpler than:
> value =  my_object.some_method(args)
> a += value[0]
> b += value[1]

You can say that here the extra lines increase the cognitive burden.
And I think I'd agree with you.

But I think there's a code-smell here. Better, I think, is to
introduce a type that supports augmented assignment. For example

> vec = Vector(a, b)
> inc = Vector(c, d)
> vec += inc

I hope this helps

-- 
Jonathan