Why do most programming languages use comma before newline, instead of after newline?

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ height:90px;width:728px;box-sizing:border-box;
}

-1

To explain why I've come up with this question, I'll explain python3's commonly used multiline list/dictionary notations and what actual syntax definition looks like.

This is the most commonly used multiline list notation in python3:

list_variable = [

    'value1',

    'value2',

    # The last comma after 'value2' is sometimes omitted.

]

And, to understand how this notation is recognized by parser, we need to look at grammar definition(link).

In the definition of python, list-like definitions are defined similar to this:

list_like: '[' [element (',' element)* [','] ] ']'

Let me explain this a little bit more, just in case you're not familiar with syntax definition or I'm a bad summarizer:

'' means it is actually a character. For example, '[' and ']' are list's ending or beginning in pure character, which will be [ 'value1', 'value2', ] in actual code.

element is their type's expected elements. for example, If it's a list, it will be a single variable. If it's a dictionary, it will be key ':' value.

means all things inside that are optional.

() means all things inside that are in one set. i.e. It all comes together.

* means a syntax set preceding that may occur 0 or more times. In this example, (',' element) may be omitted, but it also may occur 3 times.

I almost forgot to mention, that these rules are applied after whitespace managing is done.

Okay, so let's have a look at list's parsing example:

[1]

will be parsed into '[' element ']'

[1, ]

will be '[' element ',' ']'

[1, 2]

will be '[' element (',' element) ']'

[1, 2, ]

will be '[' element (',' element) ',' ']'

So, as you see, in the example 3 the comma is paired with 2, not 1.
Also, in the example the last comma is not paired with 2 - it actually is paired with nothing in terms of syntax definition.

Now the actual question is:
Is there more reasons to use comma before newline, except for the fact that most languages were using that commonly?
I think it is sensible to use comma after newline, for these reasons:

It's more similar to actual syntax definition.

It ensures that there will be always exact number of commas(number of elems - 1), and that helps when you're dealing with languages that hates additional leading comma, for example SQL.

It also is git-friendly, like comma-before notation: If you add a new element to the list, git diff will show + , new_element only.

In fact, in comma-before-newline notation if someone forgot to add a comma after old_element(Or because the language doesn't allow additional comma), someone who adds an element after that will see a git log like this:

- old_element

+ old_element,

+ new_element,

asked Nov 11 '18 at 5:58

ik1ne

10016

What if you want to add something to the front of the list?

– user2357112
Nov 11 '18 at 6:11

@user2357112 [1n,2] => [0n,1n,2], and it might show misleading git log while comma before is [1,n2] => [0,n1,n2] and creates a cleaner git log. That's one point I didn't notice. Thank you.

– ik1ne
Nov 11 '18 at 6:18

1

Between the opening and closing [ and ] brackets defining a sequence, newlines don't have much significance in Python—so I think your analysis doesn't apply. What you're talking about code layout and how it's done is hopefully by usually following some convention like PEP 8 - Style Guide for Python Code. It's most a just matter of taste and not so much about parsing efficiency. No doubt there might be some ways that would make certain modifications easier. Fine, do it, the guidelines are only suggestions.

– martineau
Nov 11 '18 at 7:15

add a comment |

-1

To explain why I've come up with this question, I'll explain python3's commonly used multiline list/dictionary notations and what actual syntax definition looks like.

This is the most commonly used multiline list notation in python3:

list_variable = [

    'value1',

    'value2',

    # The last comma after 'value2' is sometimes omitted.

]

And, to understand how this notation is recognized by parser, we need to look at grammar definition(link).

In the definition of python, list-like definitions are defined similar to this:

list_like: '[' [element (',' element)* [','] ] ']'

Let me explain this a little bit more, just in case you're not familiar with syntax definition or I'm a bad summarizer:

'' means it is actually a character. For example, '[' and ']' are list's ending or beginning in pure character, which will be [ 'value1', 'value2', ] in actual code.

element is their type's expected elements. for example, If it's a list, it will be a single variable. If it's a dictionary, it will be key ':' value.

means all things inside that are optional.

() means all things inside that are in one set. i.e. It all comes together.

* means a syntax set preceding that may occur 0 or more times. In this example, (',' element) may be omitted, but it also may occur 3 times.

I almost forgot to mention, that these rules are applied after whitespace managing is done.

Okay, so let's have a look at list's parsing example:

[1]

will be parsed into '[' element ']'

[1, ]

will be '[' element ',' ']'

[1, 2]

will be '[' element (',' element) ']'

[1, 2, ]

will be '[' element (',' element) ',' ']'

So, as you see, in the example 3 the comma is paired with 2, not 1.
Also, in the example the last comma is not paired with 2 - it actually is paired with nothing in terms of syntax definition.

It's more similar to actual syntax definition.

It ensures that there will be always exact number of commas(number of elems - 1), and that helps when you're dealing with languages that hates additional leading comma, for example SQL.

It also is git-friendly, like comma-before notation: If you add a new element to the list, git diff will show + , new_element only.

In fact, in comma-before-newline notation if someone forgot to add a comma after old_element(Or because the language doesn't allow additional comma), someone who adds an element after that will see a git log like this:

- old_element

+ old_element,

+ new_element,

asked Nov 11 '18 at 5:58

ik1ne

10016

What if you want to add something to the front of the list?

– user2357112
Nov 11 '18 at 6:11

@user2357112 [1n,2] => [0n,1n,2], and it might show misleading git log while comma before is [1,n2] => [0,n1,n2] and creates a cleaner git log. That's one point I didn't notice. Thank you.

– ik1ne
Nov 11 '18 at 6:18

1

Between the opening and closing [ and ] brackets defining a sequence, newlines don't have much significance in Python—so I think your analysis doesn't apply. What you're talking about code layout and how it's done is hopefully by usually following some convention like PEP 8 - Style Guide for Python Code. It's most a just matter of taste and not so much about parsing efficiency. No doubt there might be some ways that would make certain modifications easier. Fine, do it, the guidelines are only suggestions.

– martineau
Nov 11 '18 at 7:15

add a comment |

-1

To explain why I've come up with this question, I'll explain python3's commonly used multiline list/dictionary notations and what actual syntax definition looks like.

This is the most commonly used multiline list notation in python3:

list_variable = [

    'value1',

    'value2',

    # The last comma after 'value2' is sometimes omitted.

]

And, to understand how this notation is recognized by parser, we need to look at grammar definition(link).

In the definition of python, list-like definitions are defined similar to this:

list_like: '[' [element (',' element)* [','] ] ']'

Let me explain this a little bit more, just in case you're not familiar with syntax definition or I'm a bad summarizer:

'' means it is actually a character. For example, '[' and ']' are list's ending or beginning in pure character, which will be [ 'value1', 'value2', ] in actual code.

element is their type's expected elements. for example, If it's a list, it will be a single variable. If it's a dictionary, it will be key ':' value.

means all things inside that are optional.

() means all things inside that are in one set. i.e. It all comes together.

* means a syntax set preceding that may occur 0 or more times. In this example, (',' element) may be omitted, but it also may occur 3 times.

I almost forgot to mention, that these rules are applied after whitespace managing is done.

Okay, so let's have a look at list's parsing example:

[1]

will be parsed into '[' element ']'

[1, ]

will be '[' element ',' ']'

[1, 2]

will be '[' element (',' element) ']'

[1, 2, ]

will be '[' element (',' element) ',' ']'

So, as you see, in the example 3 the comma is paired with 2, not 1.
Also, in the example the last comma is not paired with 2 - it actually is paired with nothing in terms of syntax definition.

It's more similar to actual syntax definition.

It ensures that there will be always exact number of commas(number of elems - 1), and that helps when you're dealing with languages that hates additional leading comma, for example SQL.

It also is git-friendly, like comma-before notation: If you add a new element to the list, git diff will show + , new_element only.

In fact, in comma-before-newline notation if someone forgot to add a comma after old_element(Or because the language doesn't allow additional comma), someone who adds an element after that will see a git log like this:

- old_element

+ old_element,

+ new_element,

asked Nov 11 '18 at 5:58

ik1ne

10016

To explain why I've come up with this question, I'll explain python3's commonly used multiline list/dictionary notations and what actual syntax definition looks like.

This is the most commonly used multiline list notation in python3:

list_variable = [

    'value1',

    'value2',

    # The last comma after 'value2' is sometimes omitted.

]

And, to understand how this notation is recognized by parser, we need to look at grammar definition(link).

In the definition of python, list-like definitions are defined similar to this:

list_like: '[' [element (',' element)* [','] ] ']'

Let me explain this a little bit more, just in case you're not familiar with syntax definition or I'm a bad summarizer:

'' means it is actually a character. For example, '[' and ']' are list's ending or beginning in pure character, which will be [ 'value1', 'value2', ] in actual code.

element is their type's expected elements. for example, If it's a list, it will be a single variable. If it's a dictionary, it will be key ':' value.

means all things inside that are optional.

() means all things inside that are in one set. i.e. It all comes together.

* means a syntax set preceding that may occur 0 or more times. In this example, (',' element) may be omitted, but it also may occur 3 times.

I almost forgot to mention, that these rules are applied after whitespace managing is done.

Okay, so let's have a look at list's parsing example:

[1]

will be parsed into '[' element ']'

[1, ]

will be '[' element ',' ']'

[1, 2]

will be '[' element (',' element) ']'

[1, 2, ]

will be '[' element (',' element) ',' ']'

So, as you see, in the example 3 the comma is paired with 2, not 1.
Also, in the example the last comma is not paired with 2 - it actually is paired with nothing in terms of syntax definition.

It's more similar to actual syntax definition.

It ensures that there will be always exact number of commas(number of elems - 1), and that helps when you're dealing with languages that hates additional leading comma, for example SQL.

It also is git-friendly, like comma-before notation: If you add a new element to the list, git diff will show + , new_element only.

In fact, in comma-before-newline notation if someone forgot to add a comma after old_element(Or because the language doesn't allow additional comma), someone who adds an element after that will see a git log like this:

- old_element

+ old_element,

+ new_element,

python syntax programming-languages

asked Nov 11 '18 at 5:58

ik1ne

10016

asked Nov 11 '18 at 5:58

ik1ne

10016

asked Nov 11 '18 at 5:58

ik1ne

10016

asked Nov 11 '18 at 5:58

ik1ne

10016

asked Nov 11 '18 at 5:58

ik1ne

10016

What if you want to add something to the front of the list?

– user2357112
Nov 11 '18 at 6:11

@user2357112 [1n,2] => [0n,1n,2], and it might show misleading git log while comma before is [1,n2] => [0,n1,n2] and creates a cleaner git log. That's one point I didn't notice. Thank you.

– ik1ne
Nov 11 '18 at 6:18

1

Between the opening and closing [ and ] brackets defining a sequence, newlines don't have much significance in Python—so I think your analysis doesn't apply. What you're talking about code layout and how it's done is hopefully by usually following some convention like PEP 8 - Style Guide for Python Code. It's most a just matter of taste and not so much about parsing efficiency. No doubt there might be some ways that would make certain modifications easier. Fine, do it, the guidelines are only suggestions.

– martineau
Nov 11 '18 at 7:15

add a comment |

What if you want to add something to the front of the list?

– user2357112
Nov 11 '18 at 6:11

@user2357112 [1n,2] => [0n,1n,2], and it might show misleading git log while comma before is [1,n2] => [0,n1,n2] and creates a cleaner git log. That's one point I didn't notice. Thank you.

– ik1ne
Nov 11 '18 at 6:18

1

Between the opening and closing [ and ] brackets defining a sequence, newlines don't have much significance in Python—so I think your analysis doesn't apply. What you're talking about code layout and how it's done is hopefully by usually following some convention like PEP 8 - Style Guide for Python Code. It's most a just matter of taste and not so much about parsing efficiency. No doubt there might be some ways that would make certain modifications easier. Fine, do it, the guidelines are only suggestions.

– martineau
Nov 11 '18 at 7:15

What if you want to add something to the front of the list?

– user2357112
Nov 11 '18 at 6:11

@user2357112 [1n,2] => [0n,1n,2], and it might show misleading git log while comma before is [1,n2] => [0,n1,n2] and creates a cleaner git log. That's one point I didn't notice. Thank you.

– ik1ne
Nov 11 '18 at 6:18

Between the opening and closing [ and ] brackets defining a sequence, newlines don't have much significance in Python—so I think your analysis doesn't apply. What you're talking about code layout and how it's done is hopefully by usually following some convention like PEP 8 - Style Guide for Python Code. It's most a just matter of taste and not so much about parsing efficiency. No doubt there might be some ways that would make certain modifications easier. Fine, do it, the guidelines are only suggestions.

– martineau
Nov 11 '18 at 7:15

add a comment |

1 Answer
1

active

oldest

votes

(1) "Most" programming languages don't have any preference. It's the programmer that decides where to put commas. For the case you cite, where the language or some runtime library serializes some structure into a text string, it's a matter of preference, i.e., opinion. See (2).

(2) I, as do some others, like my programming languages to look like some familiar notation. In English prose, I write "fee, foe, fie, fum" rather than "fee ,foe ,fie ,fum" -- the comma attaches to the first of the two elements it's separating, not the second. Similarly in mathematics.

answered Jan 3 at 12:08

another-dave

1,164110

add a comment |

Your Answer

StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});

}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53246245%2fwhy-do-most-programming-languages-use-comma-before-newline-instead-of-after-new%23new-answer', 'question_page');
}
);

Post as a guest

Name

Required, but never shown

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

answered Jan 3 at 12:08

another-dave

1,164110

add a comment |

answered Jan 3 at 12:08

another-dave

1,164110

add a comment |

answered Jan 3 at 12:08

another-dave

1,164110

answered Jan 3 at 12:08

another-dave

1,164110

answered Jan 3 at 12:08

another-dave

1,164110

answered Jan 3 at 12:08

another-dave

1,164110

answered Jan 3 at 12:08

another-dave

1,164110

add a comment |

draft saved

draft discarded

Thanks for contributing an answer to Stack Overflow!

Please be sure to answer the question. Provide details and share your research!

But avoid …

Asking for help, clarification, or responding to other answers.

Making statements based on opinion; back them up with references or personal experience.

To learn more, see our tips on writing great answers.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Post as a guest

Name

Required, but never shown

Name

Required, but never shown

Name

Required, but never shown

This page is only for reference, If you need detailed information, please check here

Search This Blog

Ufyukyu