scripts/qemu-ga-client: apply (most) pylint rules

I'm only doing a very quick best-effort to preserve this script, to help
keep it from breaking further. I think there are pending ideas swirling
on the right way to implement better SDKs and better clients, and this
script might be a handy reference for those discussions. It presents
some interesting design problems, like static type safety when using a
dynamic RPC mechanism.

I believe it's worth preserving the effort and care that went into
making this script by updating it to work with our current
infrastructure. However, I am disabling the requirement for docstrings
in this file.

If you would like to help improve this script, please add docstrings
alongside any refactors or rejuvenations you might apply at that time.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210604155532.1499282-7-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

scripts/qmp/qemu-ga-client

@@ -40,6 +40,7 @@ See also: https://wiki.qemu.org/Features/QAPI/GuestAgent
 
 import argparse
 import base64
+import errno
 import os
 import random
 import sys
@@ -49,6 +50,13 @@ sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..', 'python'))
 from qemu import qmp
 
 
+# This script has not seen many patches or careful attention in quite
+# some time. If you would like to improve it, please review the design
+# carefully and add docstrings at that point in time. Until then:
+
+# pylint: disable=missing-docstring
+
+
 class QemuGuestAgent(qmp.QEMUMonitorProtocol):
     def __getattr__(self, name):
         def wrapper(**kwds):
@@ -104,7 +112,8 @@ class QemuGuestAgentClient:
 
         return '\n'.join(msgs)
 
-    def __gen_ipv4_netmask(self, prefixlen):
+    @classmethod
+    def __gen_ipv4_netmask(cls, prefixlen):
         mask = int('1' * prefixlen + '0' * (32 - prefixlen), 2)
         return '.'.join([str(mask >> 24),
                          str((mask >> 16) & 0xff),
@@ -207,10 +216,12 @@ def _cmd_fstrim(client, args):
 
 
 def _cmd_ifconfig(client, args):
+    assert not args
     print(client.ifconfig())
 
 
 def _cmd_info(client, args):
+    assert not args
     print(client.info())
 
 
@@ -239,6 +250,7 @@ def _cmd_suspend(client, args):
 
 
 def _cmd_shutdown(client, args):
+    assert not args
     client.shutdown()
 
 
@@ -246,10 +258,12 @@ _cmd_powerdown = _cmd_shutdown
 
 
 def _cmd_halt(client, args):
+    assert not args
     client.shutdown('halt')
 
 
 def _cmd_reboot(client, args):
+    assert not args
     client.shutdown('reboot')
 
 
@@ -269,8 +283,6 @@ def send_command(address, cmd, args):
     try:
         client = QemuGuestAgentClient(address)
     except OSError as err:
-        import errno
-
         print(err)
         if err.errno == errno.ECONNREFUSED:
             print('Hint: qemu is not running?')