[Python-Dev] Call for prudence about PEP-572

[Josiah Carlson]

I'm sure that only 1 or 2 people cares about my opinion on this, but I will
say that PEP 572 is taking one of my least favorite features of C/C++ and
adding it to Python. About the only good thing I can say about it is that
it might make some things more convenient to write. Worse to read, worse to
debug, and definitely less clear unless you've got a comment to explain.

At least in my case, the places I use them in C are places I feel *bad*
about later. Partly because I know I'm usually trying to over-optimize, but
partly because inline assignments are a big enough source of enough
security vulnerabilities to make me question *any* language that decides to
add them (especially 25+ years after the fact). Like... an entire async
syntax and asyncio was modified in 3.6 (coroutine trampolines are tough
without syntax, I get you, I did threads instead of dealing with them back
in '05 because I couldn't get them quite right), but inline assignments
just now? I'm at a loss.

On the Python side, I wouldn't accept any patches in any of my projects to
include := assignments, because those colons look like monitor grit, and/or
a mistake (like someone wanted != but got := ), and means that my 2.6-3.6
compatible code is now 3.7+ only. I get that language evolution is a thing
(my failures to try move *this* language in a direction I thought useful is
part of why I stopped posting here), but hiding a colon in the middle of a
line is not particularly explicit. And it definitely doesn't help for
maintaining any of the software that I'm personally responsible for
maintaining across the range of Python versions. I know you all don't care
about me and my libraries, but at least consider the thousands of other
libraries written and maintained by other folks. I mean, unless you all
want 3.7+ - only libraries.

To me, it seems like a lot of movement to support a feature that a lot of
folks straight up don't want. But I don't have my finger on the pulse of
Python or Python-dev, so maybe there are a bunch of folks coming from Go,
Pascal, Smalltalk, etc., who are jonesin' for a hit of that :=, or have
use-cases where this is a huge productivity improvement, and not a glaring
security hole waiting to get them. I just don't know. But I also don't see
a burning need; I'm 19 years in on this Python train, and I've never needed
:= before. Reading the PEP, the PR for changes to the Python standard
library, email threads in support of the feature, etc., it just doesn't
feel compelling.

My $2, because that was a bit more than 2 cents worth of opinion,
 - Josiah


On Sun, Jul 8, 2018 at 10:14 AM, Giampaolo Rodola' <g.rodola at gmail.com>
wrote:

>
>
> On Sun, Jul 8, 2018 at 6:45 PM Steve Holden <steve at holdenweb.com> wrote:
>
>> On Sun, Jul 8, 2018 at 10:41 AM, Giampaolo Rodola' <g.rodola at gmail.com>
>> wrote:
>>
>>> ​[...]
>>> I find that (space between the parentheses of a function call
>>> statement) too unnatural as a place where to put an assignment. It is
>>> not even "guarded" by a keyword like "if" or  "while" which can help as
>>> indicators that an assignment may occur. Also, I think it's way too easy to
>>> confuse it with a keyword argument:
>>>
>>>     >>> foo(x = 1)  # keyword arg
>>>     >>> foo(x := 1)  # assignment + value passing
>>> ​[...]
>>>
>>
>> ​But the PEP 8 spellings are​
>>
>>     foo(x=1)
>>
>> and
>>
>>    f(x := 1).
>>
>> The extra spacing makes it obvious that this isn't a regular named
>> argument.
>>
>
> What if the author of the code I'm reading didn't respect PEP-8? I don't
> think it's fair to invoke PEP-8 as a counter-measure to obviate a syntax
> which can clearly be mistaken with something else simply by omitting 2
> spaces. Not to mention that I don't see why anyone would want to declare a
> variable in there in the first place.
>
> --
> Giampaolo - http://grodola.blogspot.com
>
>
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