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[PULL 18/19] python/qmp.py: add casts to JSON deserialization
From: |
Philippe Mathieu-Daudé |
Subject: |
[PULL 18/19] python/qmp.py: add casts to JSON deserialization |
Date: |
Wed, 15 Jul 2020 00:21:31 +0200 |
From: John Snow <jsnow@redhat.com>
mypy and python type hints are not powerful enough to properly describe
JSON messages in Python 3.6. The best we can do, generally, is describe
them as Dict[str, Any].
Add casts to coerce this type for static analysis; but do NOT enforce
this type at runtime in any way.
Note: Python 3.8 adds a TypedDict construct which allows for the
description of more arbitrary Dictionary shapes. There is a third-party
module, "Pydantic", which is compatible with 3.6 that can be used
instead of the JSON library that parses JSON messages to fully-typed
Python objects, and may be preferable in some cases.
(That is well beyond the scope of this commit or series.)
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200710052220.3306-6-jsnow@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
python/qemu/qmp.py | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/python/qemu/qmp.py b/python/qemu/qmp.py
index ef3c919b76..1ae36050a4 100644
--- a/python/qemu/qmp.py
+++ b/python/qemu/qmp.py
@@ -13,6 +13,7 @@
import logging
from typing import (
Any,
+ cast,
Dict,
Optional,
TextIO,
@@ -130,7 +131,10 @@ def __json_read(self, only_event=False):
data = self.__sockfile.readline()
if not data:
return None
- resp = json.loads(data)
+ # By definition, any JSON received from QMP is a QMPMessage,
+ # and we are asserting only at static analysis time that it
+ # has a particular shape.
+ resp: QMPMessage = json.loads(data)
if 'event' in resp:
self.logger.debug("<<< %s", resp)
self.__events.append(resp)
@@ -262,7 +266,7 @@ def command(self, cmd, **kwds):
ret = self.cmd(cmd, kwds)
if 'error' in ret:
raise QMPResponseError(ret)
- return ret['return']
+ return cast(QMPReturnValue, ret['return'])
def pull_event(self, wait=False):
"""
--
2.21.3
- [PULL 08/19] python/machine.py: Make wait() call shutdown(), (continued)
- [PULL 08/19] python/machine.py: Make wait() call shutdown(), Philippe Mathieu-Daudé, 2020/07/14
- [PULL 09/19] tests/acceptance: wait() instead of shutdown() where appropriate, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 11/19] python/machine.py: split shutdown into hard and soft flavors, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 10/19] tests/acceptance: Don't test reboot on cubieboard, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 12/19] python/machine.py: re-add sigkill warning suppression, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 13/19] python/machine.py: change default wait timeout to 3 seconds, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 14/19] python/qmp.py: Define common types, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 15/19] iotests.py: use qemu.qmp type aliases, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 16/19] python/qmp.py: re-absorb MonitorResponseError, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 17/19] python/qmp.py: Do not return None from cmd_obj, Philippe Mathieu-Daudé, 2020/07/14
- [PULL 18/19] python/qmp.py: add casts to JSON deserialization,
Philippe Mathieu-Daudé <=
- [PULL 19/19] python/qmp.py: add QMPProtocolError, Philippe Mathieu-Daudé, 2020/07/14
- Re: [PULL 00/19] Python patches for 5.1, Peter Maydell, 2020/07/15