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From: Markus Armbruster <armbru@redhat.com>
To: John Snow <jsnow@redhat.com>
Cc: Michael Roth <michael.roth@amd.com>,
	qemu-devel@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>,
	Cleber Rosa <crosa@redhat.com>
Subject: Re: [PATCH v4 05/19] qapi/expr.py: constrain incoming expression types
Date: Fri, 26 Mar 2021 06:40:12 +0100
Message-ID: <87sg4ia2wz.fsf@dusky.pond.sub.org> (raw)
In-Reply-To: <a2e23408-1885-3ce1-8328-47f5d837971c@redhat.com> (John Snow's message of "Thu, 25 Mar 2021 16:48:57 -0400")

John Snow <jsnow@redhat.com> writes:

> On 3/25/21 10:04 AM, Markus Armbruster wrote:
>> John Snow <jsnow@redhat.com> writes:
>> 
>>> 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 | 26 +++++++++++++++++++++++---
>>>   1 file changed, 23 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
>>> index b4bbcd54c0..b75c85c160 100644
>>> --- a/scripts/qapi/expr.py
>>> +++ b/scripts/qapi/expr.py
>>> @@ -15,9 +15,18 @@
>>>   # See the COPYING file in the top-level directory.
>>>   
>>>   import re
>>> +from typing import Dict, Optional
>>>   
>>>   from .common import c_name
>>>   from .error import QAPISemError
>>> +from .parser import QAPIDoc
>>> +from .source import QAPISourceInfo
>>> +
>>> +
>>> +# Deserialized JSON objects as returned by the parser;
>>> +# The values of this mapping are not necessary to exhaustively type
>> 
>> Not necessary and also not practical with current mypy.  Correct?
>
> Neither necessary nor practical. Typing as 'object' guarantees that 
> these values will never be used in a manner not supported by all python 
> objects. Mypy does not complain, so we know that we don't misuse the type.
>
> This is helpful for proving the validity of the expr.py validator 
> itself: we know that we are not forgetting to perform type narrowing and 
> using the value contained therein inappropriately.
>
> Adding a more exhaustive typing here is impractical (for reasons we 
> learned during introspect.py), but also provides no benefit to the 
> static analysis here anyway.
>
> (None of the functions written here *assume* the shape of the structure, 
> so there are no functions that benefit from having a more laboriously 
> specified type.)
>
> If the comment needs more work, suggest away -- I tried to follow our 
> last discussion here as best as I was able.

"Needs more work" sounds like "inadequate", which isn't the case.

The comment focuses on what we need from mypy here.  We may or may not
want to hint at the other aspect: what mypy can provide.

>>> +# here, because the purpose of this module is to interrogate that type.
>>> +_JSONObject = Dict[str, object]
[...]

If we want to, maybe:

     # Deserialized JSON objects as returned by the parser.
     # The values of this mapping are not necessary to exhaustively type
     # here (and also not practical as long as mypy lacks recursive
     # types), because the purpose of this module is to interrogate that
     # type.

Thoughts?



  reply index

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-25  6:03 [PATCH v4 00/19] qapi: static typing conversion, pt3 John Snow
2021-03-25  6:03 ` [PATCH v4 01/19] qapi/expr: Comment cleanup John Snow
2021-03-25 15:41   ` Markus Armbruster
2021-03-25 20:06     ` John Snow
2021-03-25  6:03 ` [PATCH v4 02/19] flake8: Enforce shorter line length for comments and docstrings John Snow
2021-03-25 15:21   ` Markus Armbruster
2021-03-25 20:20     ` John Snow
2021-03-26  6:26       ` Markus Armbruster
2021-03-26 16:30         ` John Snow
2021-03-26 16:44           ` Peter Maydell
2021-04-08  8:32             ` Markus Armbruster
2021-04-08  8:58             ` Daniel P. Berrangé
2021-04-09  9:33               ` Markus Armbruster
2021-04-09 17:08                 ` John Snow
2021-04-08  8:35           ` Markus Armbruster
2021-04-16 12:44   ` Markus Armbruster
2021-04-16 20:25     ` John Snow
2021-04-17 10:52       ` Markus Armbruster
2021-04-20 18:06         ` John Snow
2021-03-25  6:03 ` [PATCH v4 03/19] qapi/expr.py: Remove 'info' argument from nested check_if_str John Snow
2021-03-25  6:03 ` [PATCH v4 04/19] qapi/expr.py: Check for dict instead of OrderedDict John Snow
2021-03-25  6:03 ` [PATCH v4 05/19] qapi/expr.py: constrain incoming expression types John Snow
2021-03-25 14:04   ` Markus Armbruster
2021-03-25 20:48     ` John Snow
2021-03-26  5:40       ` Markus Armbruster [this message]
2021-03-26 17:12         ` John Snow
2021-03-25  6:03 ` [PATCH v4 06/19] qapi/expr.py: Add assertion for union type 'check_dict' John Snow
2021-03-25  6:03 ` [PATCH v4 07/19] qapi/expr.py: move string check upwards in check_type John Snow
2021-03-25  6:03 ` [PATCH v4 08/19] qapi: add tests for invalid 'data' field type John Snow
2021-03-25 14:24   ` Markus Armbruster
2021-03-25  6:03 ` [PATCH v4 09/19] qapi/expr.py: Check type of 'data' member John Snow
2021-03-25 14:26   ` Markus Armbruster
2021-03-25 21:04     ` John Snow
2021-03-25  6:03 ` [PATCH v4 10/19] qapi/expr.py: Add casts in a few select cases John Snow
2021-03-25 14:33   ` Markus Armbruster
2021-03-25 23:32     ` John Snow
2021-03-25  6:03 ` [PATCH v4 11/19] qapi/expr.py: Modify check_keys to accept any Collection John Snow
2021-03-25 14:45   ` Markus Armbruster
2021-03-25 23:37     ` John Snow
2021-03-25  6:03 ` [PATCH v4 12/19] qapi/expr.py: add type hint annotations John Snow
2021-03-25  6:03 ` [PATCH v4 13/19] qapi/expr.py: Consolidate check_if_str calls in check_if John Snow
2021-03-25 15:15   ` Markus Armbruster
2021-03-26  0:07     ` John Snow
2021-03-25  6:03 ` [PATCH v4 14/19] qapi/expr.py: Remove single-letter variable John Snow
2021-03-25  6:03 ` [PATCH v4 15/19] qapi/expr.py: enable pylint checks John Snow
2021-03-25  6:03 ` [PATCH v4 16/19] qapi/expr.py: Add docstrings John Snow
2021-04-14 15:04   ` Markus Armbruster
2021-04-17  1:00     ` John Snow
2021-04-17 13:18       ` Markus Armbruster
2021-04-21  1:27         ` John Snow
2021-04-21 13:58           ` Markus Armbruster
2021-04-21 18:20             ` John Snow
2021-03-25  6:03 ` [PATCH v4 17/19] qapi/expr.py: Use tuples instead of lists for static data John Snow
2021-03-25 15:19   ` Markus Armbruster
2021-03-25  6:03 ` [PATCH v4 18/19] qapi/expr.py: move related checks inside check_xxx functions John Snow
2021-03-25  6:03 ` [PATCH v4 19/19] qapi/expr.py: Use an expression checker dispatch table John Snow
2021-03-25 15:46 ` [PATCH v4 00/19] qapi: static typing conversion, pt3 Markus Armbruster
2021-03-26  0:40 ` John Snow
2021-03-26 18:01 ` John Snow

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