[Python-Dev] A grammatical oddity: trailing commas in argument lists -- continuation (original) (raw)

Raymond Hettinger raymond.hettinger at gmail.com
Tue Dec 14 07:21:33 CET 2010

On Dec 13, 2010, at 2:16 PM, Guido van Rossum wrote:

On Mon, Dec 13, 2010 at 1:55 PM, Raymond Hettinger <raymond.hettinger at gmail.com> wrote:

It seems to me that a trailing comma in an argument list is more likely to be a user error than a deliberate comma-for-the-future. Really? Have you observed this? Even if it was inserted by mistake, it is harmless.

I only have one data point, my own mistakes. The SyntaxError has occasionally been helpful to me when working out a function signature or to detect a copy and paste error. In both cases, it meant that there was supposed to be another argument and it had been either forgotten or mispasted.

Also, if I were reviewing someone else's code and saw a trailing comma in a function definition, it would seem weird and I would wonder if the author intended a different signature.

FWIW, this isn't important to me at all. Was just noting my own experience. Don't put assign much weight to it, I don't have much of a preference either way.

Python has a long tradition of allowing redundant trailing commas in comma-separated lists, and it is habit-forming.

Right. I see that in the wild quite often and use it myself.

Raymond

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