diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 23043baa26..c6d9ae130d 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -16,11 +16,9 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
-import errno
 import os
 import re
 import subprocess
-import string
 import unittest
 import sys
 import struct
@@ -34,7 +32,7 @@
 sys.path.append(os.path.join(os.path.dirname(__file__), '..', '..', 'python'))
 from qemu import qtest
 
-assert sys.version_info >= (3,6)
+assert sys.version_info >= (3, 6)
 
 # This will not work if arguments contain spaces but is necessary if we
 # want to support the override options that ./check supports.
@@ -138,11 +136,11 @@ def qemu_img_log(*args):
     return result
 
 def img_info_log(filename, filter_path=None, imgopts=False, extra_args=[]):
-    args = [ 'info' ]
+    args = ['info']
     if imgopts:
         args.append('--image-opts')
     else:
-        args += [ '-f', imgfmt ]
+        args += ['-f', imgfmt]
     args += extra_args
     args.append(filename)
 
@@ -221,7 +219,7 @@ def cmd(self, cmd):
         # quit command is in close(), '\n' is added automatically
         assert '\n' not in cmd
         cmd = cmd.strip()
-        assert cmd != 'q' and cmd != 'quit'
+        assert cmd not in ('q', 'quit')
         self._p.stdin.write(cmd + '\n')
         self._p.stdin.flush()
         return self._read_output()
@@ -243,10 +241,8 @@ def qemu_nbd_early_pipe(*args):
         sys.stderr.write('qemu-nbd received signal %i: %s\n' %
                          (-exitcode,
                           ' '.join(qemu_nbd_args + ['--fork'] + list(args))))
-    if exitcode == 0:
-        return exitcode, ''
-    else:
-        return exitcode, subp.communicate()[0]
+
+    return exitcode, subp.communicate()[0] if exitcode else ''
 
 def qemu_nbd_popen(*args):
     '''Run qemu-nbd in daemon mode and return the parent's exit code'''
@@ -310,7 +306,7 @@ def filter_qmp(qmsg, filter_fn):
         items = qmsg.items()
 
     for k, v in items:
-        if isinstance(v, list) or isinstance(v, dict):
+        if isinstance(v, (dict, list)):
             qmsg[k] = filter_qmp(v, filter_fn)
         else:
             qmsg[k] = filter_fn(k, v)
@@ -321,7 +317,7 @@ def filter_testfiles(msg):
     return msg.replace(prefix, 'TEST_DIR/PID-')
 
 def filter_qmp_testfiles(qmsg):
-    def _filter(key, value):
+    def _filter(_key, value):
         if is_str(value):
             return filter_testfiles(value)
         return value
@@ -347,7 +343,7 @@ def filter_imgfmt(msg):
     return msg.replace(imgfmt, 'IMGFMT')
 
 def filter_qmp_imgfmt(qmsg):
-    def _filter(key, value):
+    def _filter(_key, value):
         if is_str(value):
             return filter_imgfmt(value)
         return value
@@ -358,7 +354,7 @@ def log(msg, filters=[], indent=None):
     If indent is provided, JSON serializable messages are pretty-printed.'''
     for flt in filters:
         msg = flt(msg)
-    if isinstance(msg, dict) or isinstance(msg, list):
+    if isinstance(msg, (dict, list)):
         # Python < 3.4 needs to know not to add whitespace when pretty-printing:
         separators = (', ', ': ') if indent is None else (',', ': ')
         # Don't sort if it's already sorted
@@ -369,14 +365,14 @@ def log(msg, filters=[], indent=None):
         print(msg)
 
 class Timeout:
-    def __init__(self, seconds, errmsg = "Timeout"):
+    def __init__(self, seconds, errmsg="Timeout"):
         self.seconds = seconds
         self.errmsg = errmsg
     def __enter__(self):
         signal.signal(signal.SIGALRM, self.timeout)
         signal.setitimer(signal.ITIMER_REAL, self.seconds)
         return self
-    def __exit__(self, type, value, traceback):
+    def __exit__(self, exc_type, value, traceback):
         signal.setitimer(signal.ITIMER_REAL, 0)
         return False
     def timeout(self, signum, frame):
@@ -385,7 +381,7 @@ def timeout(self, signum, frame):
 def file_pattern(name):
     return "{0}-{1}".format(os.getpid(), name)
 
-class FilePaths(object):
+class FilePaths:
     """
     FilePaths is an auto-generated filename that cleans itself up.
 
@@ -532,11 +528,11 @@ def pause_drive(self, drive, event=None):
             self.pause_drive(drive, "write_aio")
             return
         self.qmp('human-monitor-command',
-                    command_line='qemu-io %s "break %s bp_%s"' % (drive, event, drive))
+                 command_line='qemu-io %s "break %s bp_%s"' % (drive, event, drive))
 
     def resume_drive(self, drive):
         self.qmp('human-monitor-command',
-                    command_line='qemu-io %s "remove_break bp_%s"' % (drive, drive))
+                 command_line='qemu-io %s "remove_break bp_%s"' % (drive, drive))
 
     def hmp_qemu_io(self, drive, cmd):
         '''Write to a given drive using an HMP command'''
@@ -547,8 +543,8 @@ def flatten_qmp_object(self, obj, output=None, basestr=''):
         if output is None:
             output = dict()
         if isinstance(obj, list):
-            for i in range(len(obj)):
-                self.flatten_qmp_object(obj[i], output, basestr + str(i) + '.')
+            for i, atom in enumerate(obj):
+                self.flatten_qmp_object(atom, output, basestr + str(i) + '.')
         elif isinstance(obj, dict):
             for key in obj:
                 self.flatten_qmp_object(obj[key], output, basestr + key + '.')
@@ -706,9 +702,7 @@ def get_bitmap(self, node_name, bitmap_name, recording=None, bitmaps=None):
 
         for bitmap in bitmaps[node_name]:
             if bitmap.get('name', '') == bitmap_name:
-                if recording is None:
-                    return bitmap
-                elif bitmap.get('recording') == recording:
+                if recording is None or bitmap.get('recording') == recording:
                     return bitmap
         return None
 
@@ -759,12 +753,13 @@ def assert_block_path(self, root, path, expected_node, graph=None):
             assert node is not None, 'Cannot follow path %s%s' % (root, path)
 
             try:
-                node_id = next(edge['child'] for edge in graph['edges'] \
-                                             if edge['parent'] == node['id'] and
-                                                edge['name'] == child_name)
+                node_id = next(edge['child'] for edge in graph['edges']
+                               if (edge['parent'] == node['id'] and
+                                   edge['name'] == child_name))
+
+                node = next(node for node in graph['nodes']
+                            if node['id'] == node_id)
 
-                node = next(node for node in graph['nodes'] \
-                                 if node['id'] == node_id)
             except StopIteration:
                 node = None
 
@@ -782,6 +777,12 @@ def assert_block_path(self, root, path, expected_node, graph=None):
 class QMPTestCase(unittest.TestCase):
     '''Abstract base class for QMP test cases'''
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        # Many users of this class set a VM property we rely on heavily
+        # in the methods below.
+        self.vm = None
+
     def dictpath(self, d, path):
         '''Traverse a path in a nested dict'''
         for component in path.split('/'):
@@ -827,7 +828,7 @@ def assert_qmp(self, d, path, value):
         else:
             self.assertEqual(result, value,
                              '"%s" is "%s", expected "%s"'
-                                 % (path, str(result), str(value)))
+                             % (path, str(result), str(value)))
 
     def assert_no_active_block_jobs(self):
         result = self.vm.qmp('query-block-jobs')
@@ -837,15 +838,15 @@ def assert_has_block_node(self, node_name=None, file_name=None):
         """Issue a query-named-block-nodes and assert node_name and/or
         file_name is present in the result"""
         def check_equal_or_none(a, b):
-            return a == None or b == None or a == b
+            return a is None or b is None or a == b
         assert node_name or file_name
         result = self.vm.qmp('query-named-block-nodes')
         for x in result["return"]:
             if check_equal_or_none(x.get("node-name"), node_name) and \
                     check_equal_or_none(x.get("file"), file_name):
                 return
-        self.assertTrue(False, "Cannot find %s %s in result:\n%s" % \
-                (node_name, file_name, result))
+        self.fail("Cannot find %s %s in result:\n%s" %
+                  (node_name, file_name, result))
 
     def assert_json_filename_equal(self, json_filename, reference):
         '''Asserts that the given filename is a json: filename and that its
@@ -894,13 +895,13 @@ def wait_until_completed(self, drive='drive0', check_offset=True, wait=60.0,
                         self.assert_qmp(event, 'data/error', error)
                     self.assert_no_active_block_jobs()
                     return event
-                elif event['event'] == 'JOB_STATUS_CHANGE':
+                if event['event'] == 'JOB_STATUS_CHANGE':
                     self.assert_qmp(event, 'data/id', drive)
 
     def wait_ready(self, drive='drive0'):
-        '''Wait until a block job BLOCK_JOB_READY event'''
-        f = {'data': {'type': 'mirror', 'device': drive } }
-        event = self.vm.event_wait(name='BLOCK_JOB_READY', match=f)
+        """Wait until a BLOCK_JOB_READY event, and return the event."""
+        f = {'data': {'type': 'mirror', 'device': drive}}
+        return self.vm.event_wait(name='BLOCK_JOB_READY', match=f)
 
     def wait_ready_and_cancel(self, drive='drive0'):
         self.wait_ready(drive=drive)
@@ -929,7 +930,7 @@ def pause_wait(self, job_id='job0'):
                 for job in result['return']:
                     if job['device'] == job_id:
                         found = True
-                        if job['paused'] == True and job['busy'] == False:
+                        if job['paused'] and not job['busy']:
                             return job
                         break
                 assert found
@@ -1026,8 +1027,8 @@ def qemu_pipe(*args):
                             universal_newlines=True)
     exitcode = subp.wait()
     if exitcode < 0:
-        sys.stderr.write('qemu received signal %i: %s\n' % (-exitcode,
-                         ' '.join(args)))
+        sys.stderr.write('qemu received signal %i: %s\n' %
+                         (-exitcode, ' '.join(args)))
     return subp.communicate()[0]
 
 def supported_formats(read_only=False):
@@ -1059,6 +1060,7 @@ def func_wrapper(test_case: QMPTestCase, *args, **kwargs):
             if usf_list:
                 test_case.case_skip('{}: formats {} are not whitelisted'.format(
                     test_case, usf_list))
+                return None
             else:
                 return func(test_case, *args, **kwargs)
         return func_wrapper
@@ -1070,6 +1072,7 @@ def skip_if_user_is_root(func):
     def func_wrapper(*args, **kwargs):
         if os.getuid() == 0:
             case_notrun('{}: cannot be run as root'.format(args[0]))
+            return None
         else:
             return func(*args, **kwargs)
     return func_wrapper
