trailing space after parenthesized walrus operator

[xrisk]

Consider this snippet (as produced after running Black):

if (val := func()) :
    pass

Ideally, Black would remove the redundant parentheses (although I realize this is pretty hard to do).

However, why does Black insist on the single space before the terminating colon? This causes flake8 to complain (and rightly so I feel).

I skimmed through the PEP and I can’t seem to find any example where that space is used. Is this a deliberate design decision?

[xrisk]

On closer reading through the PEP, I don’t see why (val := expr) shouldn’t be transformed into val := expr. They seem to be equivalent as far as I can tell (in the context of an if-conditional). The only cases where that transformation is not valid are in top-level statements and such.

[JelleZijlstra]

We definitely shouldn't put a space before the colon, that's a bug.

I'm not as sure we should remove the parentheses, maybe it's better for clarity to have them? Black is opinionated, but we should make sure we're opinionated in the right way.

[xrisk]

@JelleZijlstra black does convert if (expr): to if expr: so…

And there are multiple examples in the PEP that omit the parentheses when there is no RHS.

[nixjdm]

The title of this issue, which I'd take as the primary point of this issue, is a duplicate of #1174. I suggest closing this issue as a duplicate and opening a new issue just for discussing whether assignment expressions in ifs should be contained in parentheses.

[ichard26]

The title of this issue, which I'd take as the primary point of this issue, is a duplicate of #1174. I suggest closing this issue as a duplicate and opening a new issue just for discussing whether assignment expressions in ifs should be contained in parentheses.

I agree and I've done that (see #1656). Thanks!