Python and trailing commas

In Python you can do this:

x = {
	'a': 1,
	'b': 2,
	'c': 3, # TAKE NOTE!
}

In almost every other language I can think of, you cannot. (In Python you can do this with lists and tuples and such as well)

I love this because I can reorder long lists without having to worry about fixing punctuation. Other people I have met hate this because of some principle or other.

Discuss? I dunno. Practicality beats pedantry here I guess.

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Published:: 7.30.07 / 1am

Category:: Programming

7 Comments

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Ankur 7.30.07 / 2am

I think it’s the same in PHP, although I hardly ever leave a trailing comma deliberately. You’re right, though - it is a little tiresome to shuffle commas around when rearranging arrays.
Ross 7.30.07 / 2am

You can add trailing commas in array defs in C, and C#, and I am fairly sure I remember this being true of Java as well.

I always thought it was to make it easier for code-generators as they would never need to worry about the trailing comma.
Pete 7.30.07 / 2am

You can do it in most languages and it will result in a warning. This is better than letting it go silently, as it could be indicative of an error — a mistype or copy & paste problem, for example.
Pete 7.30.07 / 2am

You can do it in most languages and it will result in a warning. This is better than letting it go silently, as it could be indicative of an error — a mistype or copy & paste problem, for example.

Laziness is not practicality. Especially not if it makes it easier to end up with hard-to-track bugs.
PatrickQG 7.30.07 / 4am

You can do that in javascript, except one browser (cough) then gives you a null “last” entry in the array. Of course sometimes a “trailing” comma cause other browsers to just get confused, so it’s best not.

As to ending up with hard-to-track bugs… I fail to see how this syntax could lead to them. If your language supports it, why would it lead to bugs?
Stephen 7.30.07 / 9am

You can do this in Perl, too.
b3gl 8.2.07 / 4pm

Works fine in Ruby:

x = {
“a” => 1,
“b” => 2,
“c” => 3, #comment
}

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Python and trailing commas

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