I think the only reason anyone ever used leading commas to begin with was because of languages that didn't allow a final trailing comma. In those worlds, to keep the editing smooth, people moved the commas to the beginning of the line, breaking with every comma-tradition.
I don't see a reason to make that odd style easier.
--Ned.
It seems your proposal is intended to address an aesthetic concern. Is there a case where using a leading comma would make something actually easier or more intuitive to express over the use of trailing comma?
On Fri, 2021-03-12 at 10:34 +0000, roland.puntaier--- via Python-ideas wrote:I had posted this as https://github.com/python/peps/issues/1867
The discussion so far is below.
Please make some arguments.
The major point to me is, that the symmetry is broken,
which leads to extra editing actions, like removing the comma in the first line.
I guess, this was the reason to allow the comma after the last line/entry: `[1,2,]`.
``[,1,2]`` should also be allowed, too.
The best argument is one that says: less or more effort in this or that situation.
For example, with `[1,2,]`, in line-wise formatting,
one can do without special action at the last line (removing the comma there).
All code from previous versions of Python would still work
after a `[,1,2]` syntax allowance were introduced.
=================================================================================
rpuntaie wrote:
=================================================================================
Allow initial comma
===================
Final comma works:
t = (
1,
2,
)
x = [
1,
2,
]
y = {
1,
2,
}
z = {
1:11,
2:22,
}
def fun(
a,
b,
):
pass
Initial comma does not work:
t = (
, 1
, 2
)
x = [
, 1
, 2
]
y = {
, 1
, 2
}
z = {
, 1:11
, 2:22
}
def fun(
, a
, b
):
pass
To make the syntax symmetric in this regard\
gives more freedom to format the code.
I occasionally found the restriction an unnecessary nuisance.
Before writing a PEP, I would like to discuss,
- whether something like that has been proposed already?
- what counter-arguments there could be?
=================================================================================
pxeger wrote:
=================================================================================
This is not the appropriate place to propose language changes.
Try the [python-ideas](https://mail.python.org/mailman3/lists/python-ideas.python.org/)
mailing list. However, I don't think you'll get anyone to agree.
What kind of code style are you using where you want to put commas at
the start of the line? That is totally non-standard
(see [PEP 8](https://www.python.org/dev/peps/pep-0008)), ugly, and confusing.
Arbitrary symmetry is not a good reason for changing the language. We
don't have a `tnirp` function just for the sake of symmetry with
`print` because it would be pointless and add extra complication
=================================================================================
rpuntaie wrote:
=================================================================================
I surely agree, that not ignoring the sequence is essential. Else one
would loose identifier space and thus information. I would never have
the idea to make all permutations of `p.r.i.n.t` point to the same
function. Therefore you just made a bad example.
But the comma is just a separator. Why did they allow to have the
comma before a closing bracket/parenthesis/brace? Because of symmetry
between lines, is my guess.
Occasionally one sees many spaces just the have the final comma
aligned vertically. That could be avoided by placing the comma at the
beginning.
I personally also have a macro in the editor that evaluates a line in
the parameter list, but drops an initial comma before doing that.
Therefore this is my preferred formatting.
I don't think that [PEP](https://www.python.org/dev/peps/pep-0008)
is wrong. I just don't want to be restricted by unnecessary rules.
Rules need to have a reason beyond someone dictating them. If that is
the case, I follow them, because I see the reason, but not because
someone dictates them.
I'll go to
[Python Ide as](https://mail.python.org/mailman3/lists/python-ideas.python.org/),
then. Thanks.
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