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[PATCH v3 05/16] python/qmp.py: add casts to JSON deserialization
From: |
John Snow |
Subject: |
[PATCH v3 05/16] python/qmp.py: add casts to JSON deserialization |
Date: |
Thu, 4 Jun 2020 16:22:25 -0400 |
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>
---
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 ef3c919b76c..1ae36050a42 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
- [PATCH v3 00/16] python: add mypy support to python/qemu, John Snow, 2020/06/04
- [PATCH v3 04/16] python/qmp.py: Do not return None from cmd_obj, John Snow, 2020/06/04
- [PATCH v3 03/16] python/qmp.py: re-absorb MonitorResponseError, John Snow, 2020/06/04
- [PATCH v3 05/16] python/qmp.py: add casts to JSON deserialization,
John Snow <=
- [PATCH v3 06/16] python/qmp.py: add QMPProtocolError, John Snow, 2020/06/04
- [PATCH v3 02/16] iotests.py: use qemu.qmp type aliases, John Snow, 2020/06/04
- [PATCH v3 08/16] python/machine.py: reorder __init__, John Snow, 2020/06/04
- [PATCH v3 07/16] python/machine.py: Fix monitor address typing, John Snow, 2020/06/04
- [PATCH v3 09/16] python/machine.py: Don't modify state in _base_args(), John Snow, 2020/06/04
- [PATCH v3 12/16] python/machine.py: Add _qmp access shim, John Snow, 2020/06/04