scripts/qmp-shell: refactor QMPCompleter

list is a generic type, but we expect to use strings directly. We could
subclass list[str], but pylint does not presently understand that
invocation.

Change this class to envelop a list instead of *being* a list, for
simpler mypy typing.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210607200649.1840382-25-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

scripts/qmp/qmp-shell

@@ -78,9 +78,17 @@ sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..', 'python'))
 from qemu import qmp
 
 
-class QMPCompleter(list):
-    def complete(self, text, state):
-        for cmd in self:
+class QMPCompleter:
+    # NB: Python 3.9+ will probably allow us to subclass list[str] directly,
+    # but pylint as of today does not know that List[str] is simply 'list'.
+    def __init__(self) -> None:
+        self._matches: List[str] = []
+
+    def append(self, value: str) -> None:
+        return self._matches.append(value)
+
+    def complete(self, text: str, state: int) -> Optional[str]:
+        for cmd in self._matches:
             if cmd.startswith(text):
                 if state == 0:
                     return cmd