[Python-ideas] Object grabbing (was: Re: Python-ideas Digest, Vol 114, Issue 5)

Robert van Geel robert at bign.nl
Mon May 2 10:25:10 EDT 2016

I'm receiving digests and seem to not have each individual mail, so 
here's a digested response:

One side of this that's not discussed is the possible optimization. I 
can imagine if you've got a lot of objectproperty write and -reads this 
could actually make certain use cases a lot faster such as this one, 
saving 6 opcodes:

def __init__(self, left, top, width, height, content):
     self.left = left
     self.top = top
     self.width = width
     self.height = height
     self.content = content.upper()


def __init__(self, left, top, width, height, content):
     with self:
         .left = left
         .top = top
         .width = width
         .height = height
         .content = content.upper()

The suggestion that you could accomplish this with a (peephole) 
optimizer does not seem quite correct to me:

x = myobject.b()
z = myobject.c()

does not necessarily have a consistent pointer to myobject although it 
would require some acrobatics to change them in a way that can not be 
seen by an optimizer.
You can think about exec() or even another thread intervening into a 
generator function, not something I would do but who knows.

The advantage of the construct is that the .dotted variable is 
guaranteed to point to the same physical object in memory with an 
increased reference count during the statement and a decrease happening 
at dedent.

Django would break when the 'using' keyword would be used for that, but 
the choice of keyword is arbitrary. Maybe an extended use of the 'with' 
word would be elegant, when the object would not have an __enter__ 
and/or __exit__ function it could still run for the purpose of this 
mechanism. The disadvantage is that you could not use the with construct 
for this purpose only without also triggering the __enter__ function.

On 5/2/2016 2:49 PM, python-ideas-request at python.org wrote:
> [cut]
> ----------------------------------------------------------------------
> Message: 1
> Date: Mon, 2 May 2016 14:12:28 +0200
> From: Jo?o Santos <jmcs at jsantos.eu>
> To: Robert van Geel <robert at bign.nl>
> Cc: python-ideas at python.org, "Franklin? Lee"
> 	<leewangzhong+python at gmail.com>
> Subject: Re: [Python-ideas] Object grabbing
> Message-ID:
> 	<CAH_XWH3vSfvYZit3SYdJ6K==B3iQiY58CbfTpga=shav_EaDzw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
> That is matter of experience, I already lost too many hours of my life
> looking for weird bugs caused by misspellings and missing commas, and I
> don't even work with people new to python.
> On 2 May 2016 14:04, "Robert van Geel" <robert at bign.nl> wrote:
> ------------------------------ Message: 4 Date: Mon, 2 May 2016 
> 13:48:17 +0100 From: SW <walker_s at hotmail.co.uk> To: 
> python-ideas at python.org Subject: Re: [Python-ideas] Object grabbing 
> Message-ID: <BLU436-SMTP21412FBE1145250B8A38DE8B8790 at phx.gbl> 
> Content-Type: text/plain; charset="utf-8" On 02/05/16 13:20, Koos 
> Zevenhoven wrote:
>> On Mon, May 2, 2016 at 2:48 PM, Jo?o Santos <jmcs at jsantos.eu> wrote:
>>> I think the ".d = 1" statement feels like a bug waiting to happen. It's very
>>> easy to miss a dot.
>> I suppose that's a valid concern, especially regarding assignments,
>> because the code typically would still run. But in the beginning of
>> the line, it is usually quite easy to see if there's a dot or not,
>> assuming a fixed-width font and proper indenting.
> It may be easy to see if there's a dot or not, but it may not be easy to
> tell whether there /should/ be a dot when there isn't.
> e.g.
> <snip>
>     .configuration = {'yes': 'no'}
> vs
> <snip>
>    configuration = {'yes': 'no'}
> When you might have later in the code something that assigns to a
> variable with the same name, and/or operates on that variable I think
> it'd become more difficult to determine.
> Thanks,
> S
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