Re: [PATCH 03/16] qapi/expr.py: constrain incoming expression types

[Cleber Rosa <crosa@redhat.com>]

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On Wed, Sep 23, 2020 at 03:42:24PM -0400, Eduardo Habkost wrote:
> On Tue, Sep 22, 2020 at 05:13:00PM -0400, John Snow wrote:
> > mypy does not know the types of values stored in Dicts that masquerade
> > as objects. Help the type checker out by constraining the type.
> > 
> > Signed-off-by: John Snow <jsnow@redhat.com>
> > ---
> >  scripts/qapi/expr.py | 25 ++++++++++++++++++++++---
> >  1 file changed, 22 insertions(+), 3 deletions(-)
> > 
> > diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
> > index 1872a8a3cc..f6b55a87c1 100644
> > --- a/scripts/qapi/expr.py
> > +++ b/scripts/qapi/expr.py
> > @@ -15,9 +15,17 @@
> >  # See the COPYING file in the top-level directory.
> >  
> >  import re
> > +from typing import MutableMapping, Optional
> >  
> >  from .common import c_name
> >  from .error import QAPISemError
> > +from .parser import QAPIDoc
> > +from .source import QAPISourceInfo
> > +
> > +
> > +# Expressions in their raw form are JSON-like structures with arbitrary forms.
> > +# Minimally, their top-level form must be a mapping of strings to values.
> > +Expression = MutableMapping[str, object]
> >  
> >  
> >  # Names must be letters, numbers, -, and _.  They must start with letter,
> > @@ -280,9 +288,20 @@ def check_event(expr, info):
> >  
> >  def check_exprs(exprs):
> >      for expr_elem in exprs:
> > -        expr = expr_elem['expr']
> > -        info = expr_elem['info']
> > -        doc = expr_elem.get('doc')
> > +        # Expression
> > +        assert isinstance(expr_elem['expr'], dict)
> > +        expr: Expression = expr_elem['expr']
> > +        for key in expr.keys():
> > +            assert isinstance(key, str)
> 
> mypy doesn't seem to require the key type asserts, on my testing.
>

Do you mean that mypy actually takes notice of the type assert?  And
includes that as source of information for the type check or am I
misinterpreting you?

BTW, what I understood from this assert is that a more specific
type than the MutableMapping is desirable here.  Did I get that
right John?

- Cleber.

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