Remove trailing comma in function definition on single line

[JelleZijlstra]

I would have expected

def f(x,):
    pass

to have its comma removed by Black, but that doesn't happen.

I think we should always remove the trailing comma if the function arguments fit on a single line.

(I ran into this when I removed a function's second argument and relied on Black to get rid of the trailing comma.)

[ambv]

Yes, that annoys me, too.

[ambv]

Is this related to #1288?

[felippemr]

Do we have a pr for this already? I can create one if needed.

[marctorsoc]

is this now solved? @JelleZijlstra @ambv

[mcsitter]

On master this has not been solved. I also can't see a PR for this issue. I think it would great if @felippemr could open one if he is still up for it?

[ichard26]

Closing as this issue doesn't make sense anymore after #826 and #1612 landed. The trailing comma will never be removed as it now has special meaning to Black. It is now a "magic" trailing comma and will cause the function parameter list to be exploded by Black.

def f(x,):
    pass

will be formatted (by Black 20.8b1) to:

def f(
    x,
):
    pass

---

For the reader who has randomly stumbled across this issue and wants to know about the "magic trailing comma" feature, please read its documentation.