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Date: Mon, 29 Jan 2024 17:32:59 -0800
From: Jakub Kicinski <kuba@kernel.org>
To: Donald Hunter <donald.hunter@gmail.com>
Cc: Alessandro Marcolini <alessandromarcolini99@gmail.com>,
 netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Jonathan
 Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org, Jacob Keller
 <jacob.e.keller@intel.com>, Breno Leitao <leitao@debian.org>, Jiri Pirko
 <jiri@resnulli.us>, donald.hunter@redhat.com
Subject: Re: [PATCH net-next v1 02/12] tools/net/ynl: Support sub-messages
 in nested attribute spaces
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On Sun, 28 Jan 2024 19:36:29 +0000 Donald Hunter wrote:
> > from collections import ChainMap
> >
> > class LevelChainMap(ChainMap):
> > =C2=A0=C2=A0=C2=A0 def __getitem__(self, key):
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 for mapping in self.maps:
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 try:
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 return mapping[key], self.maps[::-1].index(mapping)
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 exce=
pt KeyError:
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 pass
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return self.__missing__(key)
> >
> > =C2=A0=C2=A0=C2=A0 def get(self, key, default=3DNone, level=3DNone):
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 val, lvl =3D self[key] if ke=
y in self else (default, None)
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if level:
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if l=
vl !=3D level:
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 raise Exception("Level mismatch")
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return val, lvl
> >
> > # example usage
> > c =3D LevelChainMap({'a':1}, {'inner':{'a':1}}, {'outer': {'inner':{'a'=
:1}}})
> > print(c.get('a', level=3D2))
> > print(c.get('a', level=3D1)) #raise err
> >
> > This will leave the spec as it is and will require small changes.
> >
> > What do you think? =20
>=20
> The more I think about it, the more I agree that using path-like syntax
> in the selector is overkill. It makes sense to resolve the selector
> level from the spec and then directly access the mappings from the
> correct scope level.

Plus if we resolve from the spec that's easily reusable in C / C++=20
code gen :)