[Python-ideas] Operator for inserting an element into a list

Mikhail V mikhailwas at gmail.com
Fri Jun 15 13:25:36 EDT 2018

On Fri, Jun 15, 2018 at 6:54 PM, Chris Angelico <rosuav at gmail.com> wrote:
> On Sat, Jun 16, 2018 at 1:48 AM, Mikhail V <mikhailwas at gmail.com> wrote:
>> On Fri, Jun 15, 2018 at 5:51 AM, Michael Selik <mike at selik.org> wrote:
>>> If you would like to prove the need for this operator, one piece of evidence
>>> you can provide is a count of the number of times someone writes
>>> "list.append" for an iterable vs "+=" and encloses a str or other type in a
>>> throw-away list to effectively append.
>> That's strange idea - there is no doubt that one would use
>> list.append() and most probably
>> it is the case statistically.
>> So the question would be "what is wrong with list.append()?"
>> And as said many times, there is nothing wrong, but a lot of people
>> seem to want an in-place
>> operator for this purpose. And I can understand this, because:
>> 1. append() is _ubiquitous_
>> 2. in-place assignment form makes some emphasis on mutating, in
>> contrast to method call.
> How so? You can write "x += 1" with integers, and that doesn't mutate;
> but if you write "x.some_method()", doing nothing with the return
> value, it's fairly obvious that it's going to have side effects, most
> likely to mutate the object. Augmented assignment is no better than a
> method at that.

How it would be obvious unless you test it or already have learned by heart
that x.some_method() is in-place? For a list variable you might expect
it probably,
and if you already aware of mutability, etc.

It s just very uncommon to see standalone statements like:

for me it came into habit to think that it lacks the left-hand part and =.
Of course augmented assignment is not a panacea because it is limited only
to one operation, and the appeal of the operator itself is under question.

As for x+=1 it is implementation detail - historical idea of such operators was
mutating, so at least visually its not like a returning expression.
and I am not sure about x.method() form - was it meant to hint to the user
about anything? It seemed to me so when I started to learn Python, but its not.

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