This is a definite tangent. Trailing commas are great for reducing git
diffs, not making errors when moving things around (missing commas, which
e.g. in strings causes concatenation) but I have often wondered whether the
same could be extended to (some?) logical or arithmetic operators, in
particular:
Currently one has to write a logical expression as (using Django Q objects):
(
Q(user=user) |
Q(is_deleted=True)
)
and then removing/adding clauses is difficult, whereas if "trailing
operators" where allowed, there would be no such issue:
(
Q(user=user) |
Q(is_deleted=True) |
)
Just like with trailing commas, the "additional" operator would be ignored.
I guess (technically) it won't have to match the previous operator, it
could just be any operator with no argument after it.
Unlike with trailing comma, I think an operator on its own would not be
allowed (e.g. "(|)" or "|") as it's meaning-as-intended will be context
dependent (e.g. in this example, the correct answer is a Q() object).
I am happy to flesh this out more, but as this discussion was ongoing, I
thought I would throw it out here and see what people think? Are there
potential problems with this e.g. with parsing it?
On Fri, 12 Mar 2021 at 14:28, Paul Bryan
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. _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/E3HYA7... Code of Conduct: http://python.org/psf/codeofconduct/
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