python/qemu: make 'args' style arguments immutable

These arguments don't need to be mutable and aren't really used as
such. Clarify their types as immutable and adjust code to match where
necessary.

In general, It's probably best not to accept a user-defined mutable
object and store it as internal object state unless there's a strong
justification for doing so. Instead, try to use generic types as input
with empty tuples as the default, and coerce to list where necessary.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20201006235817.3280413-10-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

1 files changed, 17 insertions, 5 deletions

diff --git a/python/qemu/qtest.py b/python/qemu/qtest.py
index 7fde2565a0..675310d8df 100644
--- a/python/qemu/qtest.py
+++ b/python/qemu/qtest.py
@@ -19,7 +19,12 @@ subclass of QEMUMachine, respectively.
 
 import os
 import socket
-from typing import List, Optional, TextIO
+from typing import (
+    List,
+    Optional,
+    Sequence,
+    TextIO,
+)
 
 from .machine import QEMUMachine
 
@@ -99,8 +104,13 @@ class QEMUQtestMachine(QEMUMachine):
     A QEMU VM, with a qtest socket available.
     """
 
-    def __init__(self, binary, args=None, name=None, test_dir="/var/tmp",
-                 socket_scm_helper=None, sock_dir=None):
+    def __init__(self,
+                 binary: str,
+                 args: Sequence[str] = (),
+                 name: Optional[str] = None,
+                 test_dir: str = "/var/tmp",
+                 socket_scm_helper: Optional[str] = None,
+                 sock_dir: Optional[str] = None):
         if name is None:
             name = "qemu-%d" % os.getpid()
         if sock_dir is None:
@@ -114,8 +124,10 @@ class QEMUQtestMachine(QEMUMachine):
     @property
     def _base_args(self) -> List[str]:
         args = super()._base_args
-        args.extend(['-qtest', 'unix:path=' + self._qtest_path,
-                     '-accel', 'qtest'])
+        args.extend([
+            '-qtest', f"unix:path={self._qtest_path}",
+            '-accel', 'qtest'
+        ])
         return args
 
     def _pre_launch(self):