On Fri, Feb 10, 2023, 10:44 AM Markus Armbruster <arm...@redhat.com> wrote:
> John Snow <js...@redhat.com> writes:
>
> > mypy can only narrow the type of `Mapping[str, ...].keys() & Set[str]`
> > to `AbstractSet[str]` and not a `Set[str]`. As a result, if the type of
> > an expression is changed to a Mapping[], mypy is unsure if the .pop() is
> > safe.
> >
> > A forthcoming commit does exactly that, so wrap the expression in a
> > set() constructor to force the intermediate expression to be resolved as
> > a mutable type.
> >
> > Signed-off-by: John Snow <js...@redhat.com>
> > ---
> > scripts/qapi/expr.py | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
> > index b56353bdf84..af802367eff 100644
> > --- a/scripts/qapi/expr.py
> > +++ b/scripts/qapi/expr.py
> > @@ -622,8 +622,8 @@ def check_expr(expr_elem: _JSONObject) -> None:
> > if 'include' in expr:
> > return
> >
> > - metas = expr.keys() & {'enum', 'struct', 'union', 'alternate',
> > - 'command', 'event'}
> > + metas = set(expr.keys() & {
> > + 'enum', 'struct', 'union', 'alternate', 'command', 'event'})
> > if len(metas) != 1:
> > raise QAPISemError(
> > info,
> "expression must have exactly one key"
> " 'enum', 'struct', 'union', 'alternate',"
> " 'command', 'event'")
> meta = metas.pop()
>
> I'm mildly surprised that the result of operator & is considered
> immutable. How could it *not* be a freshly created set? Oh well.
>
I think because it's up to the LHS type to return the result.
Wait, maybe I can just switch the operand order, lol.
> Passing a set to set() is a no-op, so
>
> Reviewed-by: Markus Armbruster <arm...@redhat.com>
>
> Regardless, the code feels a bit too clever to me. It actually did
> already when I wrote it, but I the less clever ways I could think of
> were also much more verbose.
>
> The code checks that exactly one of a set of keys is present, and which
> one it is. Any ideas?
>
Yeah, it feels too clever but I'm not sure I know something more elegant,
really. I'll consider it while I address your feedback and prepare a respin.
>
