python: Update for pylint 2.10

A few new annoyances. Of note is the new warning for an unspecified
encoding when opening a text file, which actually does indicate a
potentially real problem; see
https://www.python.org/dev/peps/pep-0597/#motivation

Use LC_CTYPE to determine an encoding to use for interpreting QEMU's
terminal output. Note that Python states: "language code and encoding
may be None if their values cannot be determined" -- use a platform
default as a backup.

Notes: Passing encoding=None will generate a suppressed warning on
Python 3.10+ that 'None' should not be passed as the encoding
argument. This behavior may be deprecated in the future and the default
switched to be a ubiquitous UTF-8. Opting in to the locale default will
be done by passing the encoding 'locale', but that isn't available in
3.6 through 3.9. Presumably this warning will be unsuppressed some time
prior to the actual switch and we can re-investigate these issues at
that time if necessary.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-id: 20210916182248.721529-2-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/qemu/machine/machine.py

@@ -19,6 +19,7 @@ which provides facilities for managing the lifetime of a QEMU VM.
 
 import errno
 from itertools import chain
+import locale
 import logging
 import os
 import shutil
@@ -290,8 +291,12 @@ class QEMUMachine:
         return self._subp.pid
 
     def _load_io_log(self) -> None:
+        # Assume that the output encoding of QEMU's terminal output is
+        # defined by our locale. If indeterminate, allow open() to fall
+        # back to the platform default.
+        _, encoding = locale.getlocale()
         if self._qemu_log_path is not None:
-            with open(self._qemu_log_path, "r") as iolog:
+            with open(self._qemu_log_path, "r", encoding=encoding) as iolog:
                 self._iolog = iolog.read()
 
     @property

python/setup.cfg

@@ -104,6 +104,7 @@ good-names=i,
 [pylint.similarities]
 # Ignore imports when computing similarities.
 ignore-imports=yes
+ignore-signatures=yes
 
 # Minimum lines number of a similarity.
 # TODO: Remove after we opt in to Pylint 2.8.3. See commit msg.