diff --git a/ssh.py b/ssh.py
index 004fdba..1d7ebe3 100644
--- a/ssh.py
+++ b/ssh.py
@@ -28,254 +28,264 @@
 from repo_trace import Trace
 
 
-PROXY_PATH = os.path.join(os.path.dirname(__file__), 'git_ssh')
+PROXY_PATH = os.path.join(os.path.dirname(__file__), "git_ssh")
 
 
 def _run_ssh_version():
-  """run ssh -V to display the version number"""
-  return subprocess.check_output(['ssh', '-V'], stderr=subprocess.STDOUT).decode()
+    """run ssh -V to display the version number"""
+    return subprocess.check_output(
+        ["ssh", "-V"], stderr=subprocess.STDOUT
+    ).decode()
 
 
 def _parse_ssh_version(ver_str=None):
-  """parse a ssh version string into a tuple"""
-  if ver_str is None:
-    ver_str = _run_ssh_version()
-  m = re.match(r'^OpenSSH_([0-9.]+)(p[0-9]+)?\s', ver_str)
-  if m:
-    return tuple(int(x) for x in m.group(1).split('.'))
-  else:
-    return ()
+    """parse a ssh version string into a tuple"""
+    if ver_str is None:
+        ver_str = _run_ssh_version()
+    m = re.match(r"^OpenSSH_([0-9.]+)(p[0-9]+)?\s", ver_str)
+    if m:
+        return tuple(int(x) for x in m.group(1).split("."))
+    else:
+        return ()
 
 
 @functools.lru_cache(maxsize=None)
 def version():
-  """return ssh version as a tuple"""
-  try:
-    return _parse_ssh_version()
-  except FileNotFoundError:
-    print('fatal: ssh not installed', file=sys.stderr)
-    sys.exit(1)
-  except subprocess.CalledProcessError:
-    print('fatal: unable to detect ssh version', file=sys.stderr)
-    sys.exit(1)
+    """return ssh version as a tuple"""
+    try:
+        return _parse_ssh_version()
+    except FileNotFoundError:
+        print("fatal: ssh not installed", file=sys.stderr)
+        sys.exit(1)
+    except subprocess.CalledProcessError:
+        print("fatal: unable to detect ssh version", file=sys.stderr)
+        sys.exit(1)
 
 
-URI_SCP = re.compile(r'^([^@:]*@?[^:/]{1,}):')
-URI_ALL = re.compile(r'^([a-z][a-z+-]*)://([^@/]*@?[^/]*)/')
+URI_SCP = re.compile(r"^([^@:]*@?[^:/]{1,}):")
+URI_ALL = re.compile(r"^([a-z][a-z+-]*)://([^@/]*@?[^/]*)/")
 
 
 class ProxyManager:
-  """Manage various ssh clients & masters that we spawn.
+    """Manage various ssh clients & masters that we spawn.
 
-  This will take care of sharing state between multiprocessing children, and
-  make sure that if we crash, we don't leak any of the ssh sessions.
+    This will take care of sharing state between multiprocessing children, and
+    make sure that if we crash, we don't leak any of the ssh sessions.
 
-  The code should work with a single-process scenario too, and not add too much
-  overhead due to the manager.
-  """
-
-  # Path to the ssh program to run which will pass our master settings along.
-  # Set here more as a convenience API.
-  proxy = PROXY_PATH
-
-  def __init__(self, manager):
-    # Protect access to the list of active masters.
-    self._lock = multiprocessing.Lock()
-    # List of active masters (pid).  These will be spawned on demand, and we are
-    # responsible for shutting them all down at the end.
-    self._masters = manager.list()
-    # Set of active masters indexed by "host:port" information.
-    # The value isn't used, but multiprocessing doesn't provide a set class.
-    self._master_keys = manager.dict()
-    # Whether ssh masters are known to be broken, so we give up entirely.
-    self._master_broken = manager.Value('b', False)
-    # List of active ssh sesssions.  Clients will be added & removed as
-    # connections finish, so this list is just for safety & cleanup if we crash.
-    self._clients = manager.list()
-    # Path to directory for holding master sockets.
-    self._sock_path = None
-
-  def __enter__(self):
-    """Enter a new context."""
-    return self
-
-  def __exit__(self, exc_type, exc_value, traceback):
-    """Exit a context & clean up all resources."""
-    self.close()
-
-  def add_client(self, proc):
-    """Track a new ssh session."""
-    self._clients.append(proc.pid)
-
-  def remove_client(self, proc):
-    """Remove a completed ssh session."""
-    try:
-      self._clients.remove(proc.pid)
-    except ValueError:
-      pass
-
-  def add_master(self, proc):
-    """Track a new master connection."""
-    self._masters.append(proc.pid)
-
-  def _terminate(self, procs):
-    """Kill all |procs|."""
-    for pid in procs:
-      try:
-        os.kill(pid, signal.SIGTERM)
-        os.waitpid(pid, 0)
-      except OSError:
-        pass
-
-    # The multiprocessing.list() API doesn't provide many standard list()
-    # methods, so we have to manually clear the list.
-    while True:
-      try:
-        procs.pop(0)
-      except:
-        break
-
-  def close(self):
-    """Close this active ssh session.
-
-    Kill all ssh clients & masters we created, and nuke the socket dir.
+    The code should work with a single-process scenario too, and not add too
+    much overhead due to the manager.
     """
-    self._terminate(self._clients)
-    self._terminate(self._masters)
 
-    d = self.sock(create=False)
-    if d:
-      try:
-        platform_utils.rmdir(os.path.dirname(d))
-      except OSError:
-        pass
+    # Path to the ssh program to run which will pass our master settings along.
+    # Set here more as a convenience API.
+    proxy = PROXY_PATH
 
-  def _open_unlocked(self, host, port=None):
-    """Make sure a ssh master session exists for |host| & |port|.
+    def __init__(self, manager):
+        # Protect access to the list of active masters.
+        self._lock = multiprocessing.Lock()
+        # List of active masters (pid).  These will be spawned on demand, and we
+        # are responsible for shutting them all down at the end.
+        self._masters = manager.list()
+        # Set of active masters indexed by "host:port" information.
+        # The value isn't used, but multiprocessing doesn't provide a set class.
+        self._master_keys = manager.dict()
+        # Whether ssh masters are known to be broken, so we give up entirely.
+        self._master_broken = manager.Value("b", False)
+        # List of active ssh sesssions.  Clients will be added & removed as
+        # connections finish, so this list is just for safety & cleanup if we
+        # crash.
+        self._clients = manager.list()
+        # Path to directory for holding master sockets.
+        self._sock_path = None
 
-    If one doesn't exist already, we'll create it.
+    def __enter__(self):
+        """Enter a new context."""
+        return self
 
-    We won't grab any locks, so the caller has to do that.  This helps keep the
-    business logic of actually creating the master separate from grabbing locks.
-    """
-    # Check to see whether we already think that the master is running; if we
-    # think it's already running, return right away.
-    if port is not None:
-      key = '%s:%s' % (host, port)
-    else:
-      key = host
+    def __exit__(self, exc_type, exc_value, traceback):
+        """Exit a context & clean up all resources."""
+        self.close()
 
-    if key in self._master_keys:
-      return True
+    def add_client(self, proc):
+        """Track a new ssh session."""
+        self._clients.append(proc.pid)
 
-    if self._master_broken.value or 'GIT_SSH' in os.environ:
-      # Failed earlier, so don't retry.
-      return False
+    def remove_client(self, proc):
+        """Remove a completed ssh session."""
+        try:
+            self._clients.remove(proc.pid)
+        except ValueError:
+            pass
 
-    # We will make two calls to ssh; this is the common part of both calls.
-    command_base = ['ssh', '-o', 'ControlPath %s' % self.sock(), host]
-    if port is not None:
-      command_base[1:1] = ['-p', str(port)]
+    def add_master(self, proc):
+        """Track a new master connection."""
+        self._masters.append(proc.pid)
 
-    # Since the key wasn't in _master_keys, we think that master isn't running.
-    # ...but before actually starting a master, we'll double-check.  This can
-    # be important because we can't tell that that 'git@myhost.com' is the same
-    # as 'myhost.com' where "User git" is setup in the user's ~/.ssh/config file.
-    check_command = command_base + ['-O', 'check']
-    with Trace('Call to ssh (check call): %s', ' '.join(check_command)):
-      try:
-        check_process = subprocess.Popen(check_command,
-                                        stdout=subprocess.PIPE,
-                                        stderr=subprocess.PIPE)
-        check_process.communicate()  # read output, but ignore it...
-        isnt_running = check_process.wait()
+    def _terminate(self, procs):
+        """Kill all |procs|."""
+        for pid in procs:
+            try:
+                os.kill(pid, signal.SIGTERM)
+                os.waitpid(pid, 0)
+            except OSError:
+                pass
 
-        if not isnt_running:
-          # Our double-check found that the master _was_ infact running.  Add to
-          # the list of keys.
-          self._master_keys[key] = True
-          return True
-      except Exception:
-        # Ignore excpetions.  We we will fall back to the normal command and
-        # print to the log there.
-        pass
+        # The multiprocessing.list() API doesn't provide many standard list()
+        # methods, so we have to manually clear the list.
+        while True:
+            try:
+                procs.pop(0)
+            except:  # noqa: E722
+                break
 
-    command = command_base[:1] + ['-M', '-N'] + command_base[1:]
-    p = None
-    try:
-      with Trace('Call to ssh: %s', ' '.join(command)):
-        p = subprocess.Popen(command)
-    except Exception as e:
-      self._master_broken.value = True
-      print('\nwarn: cannot enable ssh control master for %s:%s\n%s'
-            % (host, port, str(e)), file=sys.stderr)
-      return False
+    def close(self):
+        """Close this active ssh session.
 
-    time.sleep(1)
-    ssh_died = (p.poll() is not None)
-    if ssh_died:
-      return False
+        Kill all ssh clients & masters we created, and nuke the socket dir.
+        """
+        self._terminate(self._clients)
+        self._terminate(self._masters)
 
-    self.add_master(p)
-    self._master_keys[key] = True
-    return True
+        d = self.sock(create=False)
+        if d:
+            try:
+                platform_utils.rmdir(os.path.dirname(d))
+            except OSError:
+                pass
 
-  def _open(self, host, port=None):
-    """Make sure a ssh master session exists for |host| & |port|.
+    def _open_unlocked(self, host, port=None):
+        """Make sure a ssh master session exists for |host| & |port|.
 
-    If one doesn't exist already, we'll create it.
+        If one doesn't exist already, we'll create it.
 
-    This will obtain any necessary locks to avoid inter-process races.
-    """
-    # Bail before grabbing the lock if we already know that we aren't going to
-    # try creating new masters below.
-    if sys.platform in ('win32', 'cygwin'):
-      return False
+        We won't grab any locks, so the caller has to do that.  This helps keep
+        the business logic of actually creating the master separate from
+        grabbing locks.
+        """
+        # Check to see whether we already think that the master is running; if
+        # we think it's already running, return right away.
+        if port is not None:
+            key = "%s:%s" % (host, port)
+        else:
+            key = host
 
-    # Acquire the lock.  This is needed to prevent opening multiple masters for
-    # the same host when we're running "repo sync -jN" (for N > 1) _and_ the
-    # manifest <remote fetch="ssh://xyz"> specifies a different host from the
-    # one that was passed to repo init.
-    with self._lock:
-      return self._open_unlocked(host, port)
+        if key in self._master_keys:
+            return True
 
-  def preconnect(self, url):
-    """If |uri| will create a ssh connection, setup the ssh master for it."""
-    m = URI_ALL.match(url)
-    if m:
-      scheme = m.group(1)
-      host = m.group(2)
-      if ':' in host:
-        host, port = host.split(':')
-      else:
-        port = None
-      if scheme in ('ssh', 'git+ssh', 'ssh+git'):
-        return self._open(host, port)
-      return False
+        if self._master_broken.value or "GIT_SSH" in os.environ:
+            # Failed earlier, so don't retry.
+            return False
 
-    m = URI_SCP.match(url)
-    if m:
-      host = m.group(1)
-      return self._open(host)
+        # We will make two calls to ssh; this is the common part of both calls.
+        command_base = ["ssh", "-o", "ControlPath %s" % self.sock(), host]
+        if port is not None:
+            command_base[1:1] = ["-p", str(port)]
 
-    return False
+        # Since the key wasn't in _master_keys, we think that master isn't
+        # running... but before actually starting a master, we'll double-check.
+        # This can be important because we can't tell that that 'git@myhost.com'
+        # is the same as 'myhost.com' where "User git" is setup in the user's
+        # ~/.ssh/config file.
+        check_command = command_base + ["-O", "check"]
+        with Trace("Call to ssh (check call): %s", " ".join(check_command)):
+            try:
+                check_process = subprocess.Popen(
+                    check_command,
+                    stdout=subprocess.PIPE,
+                    stderr=subprocess.PIPE,
+                )
+                check_process.communicate()  # read output, but ignore it...
+                isnt_running = check_process.wait()
 
-  def sock(self, create=True):
-    """Return the path to the ssh socket dir.
+                if not isnt_running:
+                    # Our double-check found that the master _was_ infact
+                    # running.  Add to the list of keys.
+                    self._master_keys[key] = True
+                    return True
+            except Exception:
+                # Ignore excpetions.  We we will fall back to the normal command
+                # and print to the log there.
+                pass
 
-    This has all the master sockets so clients can talk to them.
-    """
-    if self._sock_path is None:
-      if not create:
-        return None
-      tmp_dir = '/tmp'
-      if not os.path.exists(tmp_dir):
-        tmp_dir = tempfile.gettempdir()
-      if version() < (6, 7):
-        tokens = '%r@%h:%p'
-      else:
-        tokens = '%C'  # hash of %l%h%p%r
-      self._sock_path = os.path.join(
-          tempfile.mkdtemp('', 'ssh-', tmp_dir),
-          'master-' + tokens)
-    return self._sock_path
+        command = command_base[:1] + ["-M", "-N"] + command_base[1:]
+        p = None
+        try:
+            with Trace("Call to ssh: %s", " ".join(command)):
+                p = subprocess.Popen(command)
+        except Exception as e:
+            self._master_broken.value = True
+            print(
+                "\nwarn: cannot enable ssh control master for %s:%s\n%s"
+                % (host, port, str(e)),
+                file=sys.stderr,
+            )
+            return False
+
+        time.sleep(1)
+        ssh_died = p.poll() is not None
+        if ssh_died:
+            return False
+
+        self.add_master(p)
+        self._master_keys[key] = True
+        return True
+
+    def _open(self, host, port=None):
+        """Make sure a ssh master session exists for |host| & |port|.
+
+        If one doesn't exist already, we'll create it.
+
+        This will obtain any necessary locks to avoid inter-process races.
+        """
+        # Bail before grabbing the lock if we already know that we aren't going
+        # to try creating new masters below.
+        if sys.platform in ("win32", "cygwin"):
+            return False
+
+        # Acquire the lock.  This is needed to prevent opening multiple masters
+        # for the same host when we're running "repo sync -jN" (for N > 1) _and_
+        # the manifest <remote fetch="ssh://xyz"> specifies a different host
+        # from the one that was passed to repo init.
+        with self._lock:
+            return self._open_unlocked(host, port)
+
+    def preconnect(self, url):
+        """If |uri| will create a ssh connection, setup the ssh master for it."""  # noqa: E501
+        m = URI_ALL.match(url)
+        if m:
+            scheme = m.group(1)
+            host = m.group(2)
+            if ":" in host:
+                host, port = host.split(":")
+            else:
+                port = None
+            if scheme in ("ssh", "git+ssh", "ssh+git"):
+                return self._open(host, port)
+            return False
+
+        m = URI_SCP.match(url)
+        if m:
+            host = m.group(1)
+            return self._open(host)
+
+        return False
+
+    def sock(self, create=True):
+        """Return the path to the ssh socket dir.
+
+        This has all the master sockets so clients can talk to them.
+        """
+        if self._sock_path is None:
+            if not create:
+                return None
+            tmp_dir = "/tmp"
+            if not os.path.exists(tmp_dir):
+                tmp_dir = tempfile.gettempdir()
+            if version() < (6, 7):
+                tokens = "%r@%h:%p"
+            else:
+                tokens = "%C"  # hash of %l%h%p%r
+            self._sock_path = os.path.join(
+                tempfile.mkdtemp("", "ssh-", tmp_dir), "master-" + tokens
+            )
+        return self._sock_path