diff --git a/.github/workflows/python-sanity.yml b/.github/workflows/python-sanity.yml
index dd5b953..3de7b03 100644
--- a/.github/workflows/python-sanity.yml
+++ b/.github/workflows/python-sanity.yml
@@ -36,4 +36,4 @@ jobs:
         run: python3 -m flake8 nvmet/ nvmetcli
 
       - name: pylint
-        run: python3 -m pylint --disable=all --enable=E nvmet/ nvmetcli
+        run: python3 -m pylint --enable=E nvmet/ nvmetcli
diff --git a/nvmet/__init__.py b/nvmet/__init__.py
index facd019..7566dbd 100644
--- a/nvmet/__init__.py
+++ b/nvmet/__init__.py
@@ -1,2 +1,5 @@
-from .nvme import Root, Subsystem, Namespace, Port, Host, Referral, ANAGroup, \
-    Passthru, DEFAULT_SAVE_FILE   # noqa: F401
+"""
+NVMe-oF Target configfs-based kernel driver API
+"""
+from .nvme import (ANAGroup, DEFAULT_SAVE_FILE, Host, Namespace,  # noqa: F401
+                   Passthru, Port, Referral, Root, Subsystem, CFSError)
diff --git a/nvmet/nvme.py b/nvmet/nvme.py
index 2bc0cb8..5bc1485 100644
--- a/nvmet/nvme.py
+++ b/nvmet/nvme.py
@@ -24,7 +24,16 @@
 import json
 import subprocess
 import shlex
+from doctest import testmod
 from glob import iglob as glob
+try:
+    from kmodpy import kmod
+except ImportError:
+    kmod = None
+try:
+    import kmod as kmod_ctypes
+except ImportError:
+    kmod_ctypes = None
 
 DEFAULT_SAVE_FILE = '/etc/nvmet/config.json'
 
@@ -33,7 +42,6 @@ class CFSError(Exception):
     '''
     Generic slib error.
     '''
-    pass
 
 
 class CFSNotFound(CFSError):
@@ -41,12 +49,16 @@ class CFSNotFound(CFSError):
     The underlying configfs object does not exist. Happens when
     calling methods of an object that is instantiated but have
     been deleted from configfs, or when trying to lookup an
+
     object that does not exist.
     '''
-    pass
 
 
-class CFSNode(object):
+class CFSNode:
+    '''
+    A node in the configfs filesystem.
+    This is the base class for all other objects.
+    '''
 
     configfs_dir = '/sys/kernel/config/nvmet'
 
@@ -56,12 +68,21 @@ def __init__(self):
         self.attr_groups = []
 
     def __eq__(self, other):
+        '''
+        Checks if two CFSNode objects are equal.
+        '''
         return self._path == other._path
 
     def __ne__(self, other):
+        '''
+        Checks if two CFSNode objects are not equal.
+        '''
         return self._path != other._path
 
     def _get_path(self):
+        '''
+        Returns the path of the CFSNode.
+        '''
         return self._path
 
     def _create_in_cfs(self, mode):
@@ -73,29 +94,35 @@ def _create_in_cfs(self, mode):
         create -> create the node which must not exist beforehand
         '''
         if mode not in ['any', 'lookup', 'create']:
-            raise CFSError("Invalid mode: %s" % mode)
+            raise CFSError(f"Invalid mode: {mode}")
         if self.exists and mode == 'create':
-            raise CFSError("This %s already exists in configFS" %
-                           self.__class__.__name__)
-        elif not self.exists and mode == 'lookup':
-            raise CFSNotFound("No such %s in configfs: %s" %
-                              (self.__class__.__name__, self.path))
+            raise CFSError(f"This {self.__class__.__name__} already "
+                           f"exists in configFS")
+        if not self.exists and mode == 'lookup':
+            raise CFSNotFound(f"No such {self.__class__.__name__} in "
+                              f"configfs: {self.path}")
 
         if not self.exists:
             try:
                 os.mkdir(self.path)
-            except Exception:
-                raise CFSError("Could not create %s in configFS" %
-                               self.__class__.__name__)
+            except Exception as exc:
+                raise CFSError(f"Could not create {self.__class__.__name__}"
+                               f" in configFS") from exc
         self.get_enable()
 
     def _exists(self):
+        '''
+        Returns True if the CFSNode exists, False otherwise.
+        '''
         return os.path.isdir(self.path)
 
     def _check_self(self):
+        '''
+        Checks if the CFSNode exists.
+        '''
         if not self.exists:
-            raise CFSNotFound("This %s does not exist in configFS" %
-                              self.__class__.__name__)
+            raise CFSNotFound(f"This {self.__class__.__name__} does not "
+                              f"exist in configFS")
 
     def list_attrs(self, group, writable=None):
         '''
@@ -109,7 +136,7 @@ def list_attrs(self, group, writable=None):
         self._check_self()
 
         names = [os.path.basename(name).split('_', 1)[1]
-                 for name in glob("%s/%s_*" % (self._path, group))
+                 for name in glob(f"{self._path}/{group}_*")
                  if os.path.isfile(name)]
 
         if writable is True:
@@ -123,7 +150,10 @@ def list_attrs(self, group, writable=None):
         return names
 
     def _attr_is_writable(self, group, name):
-        s = os.stat("%s/%s_%s" % (self._path, group, name))
+        '''
+        Returns True if the attribute is writable, False otherwise.
+        '''
+        s = os.stat(f"{self._path}/{group}_{name}")
         return s[stat.ST_MODE] & stat.S_IWUSR
 
     def set_attr(self, group, attribute, value):
@@ -136,20 +166,20 @@ def set_attr(self, group, attribute, value):
         @type value: string
         '''
         self._check_self()
-        path = "%s/%s_%s" % (self.path, str(group), str(attribute))
+        path = f"{self.path}/{str(group)}_{str(attribute)}"
 
         if not os.path.isfile(path):
-            raise CFSError("Cannot find attribute: %s" % path)
+            raise CFSError(f"Cannot find attribute: {path}")
 
         if self._enable:
-            raise CFSError("Cannot set attribute while %s is enabled" %
-                           self.__class__.__name__)
+            raise CFSError(f"Cannot set attribute while "
+                           f"{self.__class__.__name__} is enabled")
 
         try:
-            with open(path, 'w') as file_fd:
+            with open(path, 'w', encoding="utf-8") as file_fd:
                 file_fd.write(str(value))
-        except Exception as e:
-            raise CFSError("Cannot set attribute %s: %s" % (path, e))
+        except OSError as e:
+            raise CFSError(f"Cannot set attribute {path}: {e}") from e
 
     def get_attr(self, group, attribute):
         '''
@@ -159,36 +189,41 @@ def get_attr(self, group, attribute):
         @return: The named attribute's value, as a string.
         '''
         self._check_self()
-        path = "%s/%s_%s" % (self.path, str(group), str(attribute))
+        path = f"{self.path}/{str(group)}_{str(attribute)}"
         if not os.path.isfile(path):
-            raise CFSError("Cannot find attribute: %s" % path)
+            raise CFSError(f"Cannot find attribute: {path}")
 
-        with open(path, 'r') as file_fd:
+        with open(path, 'r', encoding="utf-8") as file_fd:
             return file_fd.read().strip()
 
     def get_enable(self):
+        '''
+        Returns the value of the 'enable' attribute.
+        '''
         self._check_self()
-        path = "%s/enable" % self.path
+        path = f"{self.path}/enable"
         if not os.path.isfile(path):
             return None
 
-        with open(path, 'r') as file_fd:
+        with open(path, 'r', encoding="utf-8") as file_fd:
             self._enable = int(file_fd.read().strip())
         return self._enable
 
     def set_enable(self, value):
+        '''
+        Sets the value of the 'enable' attribute.
+        '''
         self._check_self()
-        path = "%s/enable" % self.path
+        path = f"{self.path}/enable"
 
         if not os.path.isfile(path) or self._enable is None:
-            raise CFSError("Cannot enable %s" % self.path)
+            raise CFSError(f"Cannot enable {self.path}")
 
         try:
-            with open(path, 'w') as file_fd:
+            with open(path, 'w', encoding="utf-8") as file_fd:
                 file_fd.write(str(value))
-        except Exception as e:
-            raise CFSError("Cannot enable %s: %s (%s)" %
-                           (self.path, e, value))
+        except OSError as e:
+            raise CFSError(f"Cannot enable {self.path}: {e} ({value})") from e
         self._enable = value
 
     def delete(self):
@@ -209,6 +244,9 @@ def delete(self):
                       + " any other means, it will be False.")
 
     def dump(self):
+        '''
+        Returns a dict with the config of the object.
+        '''
         d = {}
         for group in self.attr_groups:
             a = {}
@@ -220,6 +258,9 @@ def dump(self):
         return d
 
     def _setup_attrs(self, attr_dict, err_func):
+        '''
+        Set up attributes from a dict.
+        '''
         for group in self.attr_groups:
             for name, value in attr_dict.get(group, {}).items():
                 try:
@@ -232,53 +273,55 @@ def _setup_attrs(self, attr_dict, err_func):
 
 
 class Root(CFSNode):
+    '''
+    The root of the NVMe target configfs hierarchy.
+    '''
     def __init__(self):
-        super(Root, self).__init__()
+        super().__init__()
 
         self.attr_groups = ['discovery']
         if not os.path.isdir(self.configfs_dir):
             self._modprobe('nvmet')
 
         if not os.path.isdir(self.configfs_dir):
-            raise CFSError("%s does not exist.  Giving up." %
-                           self.configfs_dir)
+            raise CFSError(f"{self.configfs_dir} does not exist.  Giving up.")
 
         self._path = self.configfs_dir
         self._create_in_cfs('lookup')
 
     def _modprobe(self, modname):
-        try:
-            from kmodpy import kmod
-
+        '''
+        Load a kernel module.
+        '''
+        if kmod:
             try:
                 kmod.Kmod().modprobe(modname, quiet=True)
+                return
             except kmod.KmodError:
                 pass
-        except ImportError:
-            # Try the ctypes library included with the libkmod itself.
+
+        if kmod_ctypes:
             try:
-                import kmod
+                kmod_ctypes.Kmod().modprobe(modname)
+                return
+            except OSError:
+                pass
 
-                try:
-                    kmod.Kmod().modprobe(modname)
-                except Exception:
-                    pass
-            except ImportError:
-                # Try the binary specified in /proc
-                try:
-                    modprobe_cmd = None
-                    with open('/proc/sys/kernel/modprobe', 'r') as f:
-                        modprobe_cmd = f.read()
-                    if modprobe_cmd:
-                        subprocess.run(shlex.split(modprobe_cmd) + [modname],
-                                       check=False)
-                except Exception:
-                    pass
+        # Try the binary specified in /proc
+        try:
+            modprobe_cmd = None
+            with open('/proc/sys/kernel/modprobe', 'r', encoding="utf-8") as f:
+                modprobe_cmd = f.read()
+            if modprobe_cmd:
+                subprocess.run(shlex.split(modprobe_cmd) + [modname],
+                               check=False)
+        except OSError:
+            pass
 
     def _list_subsystems(self):
         self._check_self()
 
-        for d in os.listdir("%s/subsystems/" % self._path):
+        for d in os.listdir(f"{self._path}/subsystems/"):
             yield Subsystem(d, 'lookup')
 
     subsystems = property(_list_subsystems,
@@ -287,7 +330,7 @@ def _list_subsystems(self):
     def _list_ports(self):
         self._check_self()
 
-        for d in os.listdir("%s/ports/" % self._path):
+        for d in os.listdir(f"{self._path}/ports/"):
             yield Port(d, 'lookup')
 
     ports = property(_list_ports,
@@ -296,7 +339,7 @@ def _list_ports(self):
     def _list_hosts(self):
         self._check_self()
 
-        for h in os.listdir("%s/hosts/" % self._path):
+        for h in os.listdir(f"{self._path}/hosts/"):
             yield Host(h, 'lookup')
 
     hosts = property(_list_hosts,
@@ -316,7 +359,7 @@ def save_to_file(self, savefile=None):
         if not os.path.exists(savefile_dir):
             os.makedirs(savefile_dir)
 
-        with open(savefile + ".temp", "w+") as f:
+        with open(savefile + ".temp", "w+", encoding="utf-8") as f:
             os.fchmod(f.fileno(), stat.S_IRUSR | stat.S_IWUSR)
             f.write(json.dumps(self.dump(), sort_keys=True, indent=2))
             f.write("\n")
@@ -371,24 +414,24 @@ def err_func(err_str):
         # Create the hosts first because the subsystems reference them
         for index, t in enumerate(config.get('hosts', [])):
             if 'nqn' not in t:
-                err_func("'nqn' not defined in host %d" % index)
+                err_func(f"'nqn' not defined in host {index}")
                 continue
 
             Host.setup(t, err_func)
 
         for index, t in enumerate(config.get('subsystems', [])):
             if 'nqn' not in t:
-                err_func("'nqn' not defined in subsystem %d" % index)
+                err_func(f"'nqn' not defined in subsystem {index}")
                 continue
 
             Subsystem.setup(t, err_func)
 
         for index, t in enumerate(config.get('ports', [])):
             if 'portid' not in t:
-                err_func("'portid' not defined in port %d" % index)
+                err_func(f"'portid' not defined in port {index}")
                 continue
 
-            Port.setup(self, t, err_func)
+            Port.setup(t, err_func)
 
         return errors
 
@@ -404,13 +447,13 @@ def restore_from_file(self, savefile=None, clear_existing=True,
         else:
             savefile = DEFAULT_SAVE_FILE
 
-        with open(savefile, "r") as f:
+        with open(savefile, "r", encoding="utf-8") as f:
             config = json.loads(f.read())
             return self.restore(config, clear_existing=clear_existing,
                                 abort_on_error=abort_on_error)
 
     def dump(self):
-        d = super(Root, self).dump()
+        d = super().dump()
         d['subsystems'] = [s.dump() for s in self.subsystems]
         d['ports'] = [p.dump() for p in self.ports]
         d['hosts'] = [h.dump() for h in self.hosts]
@@ -424,7 +467,7 @@ class Subsystem(CFSNode):
     '''
 
     def __repr__(self):
-        return "<Subsystem %s>" % self.nqn
+        return f"<Subsystem {self.nqn}>"
 
     def __init__(self, nqn=None, mode='any'):
         '''
@@ -439,7 +482,7 @@ def __init__(self, nqn=None, mode='any'):
         @type mode:string
         @return: A Subsystem object.
         '''
-        super(Subsystem, self).__init__()
+        super().__init__()
 
         if nqn is None:
             if mode == 'lookup':
@@ -448,13 +491,16 @@ def __init__(self, nqn=None, mode='any'):
 
         self.nqn = nqn
         self.attr_groups = ['attr']
-        self._path = "%s/subsystems/%s" % (self.configfs_dir, nqn)
+        self._path = f"{self.configfs_dir}/subsystems/{nqn}"
         self._create_in_cfs(mode)
 
     def _generate_nqn(self):
+        '''
+        Generates a new NQN.
+        '''
         prefix = "nqn.2014-08.org.nvmexpress:NVMf:uuid"
         name = str(uuid.uuid4())
-        return "%s:%s" % (prefix, name)
+        return f"{prefix}:{name}"
 
     def delete(self):
         '''
@@ -467,17 +513,23 @@ def delete(self):
             ns.delete()
         for h in self.allowed_hosts:
             self.remove_allowed_host(h)
-        super(Subsystem, self).delete()
+        super().delete()
 
     def _list_namespaces(self):
+        '''
+        Lists the namespaces of the subsystem.
+        '''
         self._check_self()
-        for d in os.listdir("%s/namespaces/" % self._path):
+        for d in os.listdir(f"{self._path}/namespaces/"):
             yield Namespace(self, int(d), 'lookup')
 
     namespaces = property(_list_namespaces,
                           doc="Get the list of Namespaces for the Subsystem.")
 
     def _get_passthru(self):
+        '''
+        Returns the passthru object of the subsystem.
+        '''
         self._check_self()
         return Passthru(self)
 
@@ -485,8 +537,11 @@ def _get_passthru(self):
                         doc="Get the passthru node for the subsystem")
 
     def _list_allowed_hosts(self):
+        '''
+        Lists the allowed hosts of the subsystem.
+        '''
         return [os.path.basename(name)
-                for name in os.listdir("%s/allowed_hosts/" % self._path)]
+                for name in os.listdir(f"{self._path}/allowed_hosts/")]
 
     allowed_hosts = property(_list_allowed_hosts,
                              doc="Get the list of Allowed Hosts for the "
@@ -497,21 +552,24 @@ def add_allowed_host(self, nqn):
         Enable access for the host identified by I{nqn} to the Subsystem
         '''
         try:
-            os.symlink("%s/hosts/%s" % (self.configfs_dir, nqn),
-                       "%s/allowed_hosts/%s" % (self._path, nqn))
-        except Exception as e:
-            raise CFSError("Could not symlink %s in configFS: %s" % (nqn, e))
+            os.symlink(f"{self.configfs_dir}/hosts/{nqn}",
+                       f"{self._path}/allowed_hosts/{nqn}")
+        except OSError as e:
+            raise CFSError(f"Could not symlink {nqn} in configFS: {e}") from e
 
     def remove_allowed_host(self, nqn):
         '''
         Disable access for the host identified by I{nqn} to the Subsystem
         '''
         try:
-            os.unlink("%s/allowed_hosts/%s" % (self._path, nqn))
-        except Exception as e:
-            raise CFSError("Could not unlink %s in configFS: %s" % (nqn, e))
+            os.unlink(f"{self._path}/allowed_hosts/{nqn}")
+        except OSError as e:
+            raise CFSError(f"Could not unlink {nqn} in configFS: {e}") from e
 
     def has_passthru(self):
+        '''
+        Check if the subsystem has a passthru node.
+        '''
         return os.path.isdir(os.path.join(self.path, "passthru"))
 
     @classmethod
@@ -529,7 +587,7 @@ def setup(cls, t, err_func):
         try:
             s = Subsystem(t['nqn'])
         except CFSError as e:
-            err_func("Could not create Subsystem object: %s" % e)
+            err_func(f"Could not create Subsystem object: {e}")
             return
 
         for ns in t.get('namespaces', []):
@@ -542,7 +600,7 @@ def setup(cls, t, err_func):
         s._setup_attrs(t, err_func)
 
     def dump(self):
-        d = super(Subsystem, self).dump()
+        d = super().dump()
         d['nqn'] = self.nqn
         d['namespaces'] = [ns.dump() for ns in self.namespaces]
         d['allowed_hosts'] = self.allowed_hosts
@@ -560,7 +618,7 @@ class Namespace(CFSNode):
     MAX_NSID = 8192
 
     def __repr__(self):
-        return "<Namespace %d>" % self.nsid
+        return f"<Namespace {self.nsid}>"
 
     def __init__(self, subsystem, nsid=None, mode='any'):
         '''
@@ -576,7 +634,7 @@ def __init__(self, subsystem, nsid=None, mode='any'):
         @type mode:string
         @return: A Namespace object.
         '''
-        super(Namespace, self).__init__()
+        super().__init__()
 
         if not isinstance(subsystem, Subsystem):
             raise CFSError("Invalid parent class")
@@ -591,38 +649,50 @@ def __init__(self, subsystem, nsid=None, mode='any'):
                     nsid = index
                     break
             if nsid is None:
-                raise CFSError("All NSIDs 1-%d in use" % self.MAX_NSID)
+                raise CFSError(f"All NSIDs 1-{self.MAX_NSID} in use")
         else:
             nsid = int(nsid)
             if nsid < 1 or nsid > self.MAX_NSID:
-                raise CFSError("NSID must be 1 to %d" % self.MAX_NSID)
+                raise CFSError(f"NSID must be 1 to {self.MAX_NSID}")
 
         self.attr_groups = ['device', 'ana', 'resv']
         self._subsystem = subsystem
         self._nsid = nsid
-        self._path = "%s/namespaces/%d" % (self.subsystem.path, self.nsid)
+        self._path = f"{self.subsystem.path}/namespaces/{self.nsid}"
         self._create_in_cfs(mode)
 
     def _get_subsystem(self):
+        '''
+        Returns the parent subsystem.
+        '''
         return self._subsystem
 
     def _get_nsid(self):
+        '''
+        Returns the namespace ID.
+        '''
         return self._nsid
 
     def _get_grpid(self):
+        '''
+        Returns the ANA group ID.
+        '''
         self._check_self()
         _grpid = 0
-        path = "%s/ana_grpid" % self.path
+        path = f"{self.path}/ana_grpid"
         if os.path.isfile(path):
-            with open(path, 'r') as file_fd:
+            with open(path, 'r', encoding="utf-8") as file_fd:
                 _grpid = int(file_fd.read().strip())
         return _grpid
 
     def set_grpid(self, grpid):
+        '''
+        Sets the ANA group ID.
+        '''
         self._check_self()
-        path = "%s/ana_grpid" % self.path
+        path = f"{self.path}/ana_grpid"
         if os.path.isfile(path):
-            with open(path, 'w') as file_fd:
+            with open(path, 'w', encoding="utf-8") as file_fd:
                 file_fd.write(str(grpid))
 
     grpid = property(_get_grpid, doc="Get the ANA Group ID.")
@@ -646,7 +716,7 @@ def setup(cls, subsys, n, err_func):
         try:
             ns = Namespace(subsys, n['nsid'])
         except CFSError as e:
-            err_func("Could not create Namespace object: %s" % e)
+            err_func(f"Could not create Namespace object: {e}")
             return
 
         ns._setup_attrs(n, err_func)
@@ -654,7 +724,10 @@ def setup(cls, subsys, n, err_func):
             ns.set_grpid(int(n['ana_grpid']))
 
     def dump(self):
-        d = super(Namespace, self).dump()
+        '''
+        Returns a dict with the config of the object.
+        '''
+        d = super().dump()
         d['nsid'] = self.nsid
         d['ana_grpid'] = self.grpid
         return d
@@ -663,6 +736,7 @@ def dump(self):
 class Passthru(CFSNode):
     '''
     This is an interface to a NVMe passthru in ConfigFS.
+    A Passthru is identified by its parent Subsystem.
     '''
 
     def __init__(self, subsystem):
@@ -670,16 +744,19 @@ def __init__(self, subsystem):
         @param subsystem: The parent Subsystem object.
         @return: A Passthru object.
         '''
-        super(Passthru, self).__init__()
-        self._path = "%s/passthru" % (subsystem.path)
+        super().__init__()
+        self._path = f"{subsystem.path}/passthru"
         self.attr_groups = ['device']
 
     def _get_clear_ids(self):
+        '''
+        Get the passthru namespace clear_ids attribute.
+        '''
         self._check_self()
-        path = "%s/clear_ids" % self.path
+        path = f"{self.path}/clear_ids"
         _ids = 0
         if os.path.isfile(path):
-            with open(path, 'r') as file_fd:
+            with open(path, 'r', encoding="utf-8") as file_fd:
                 _ids = int(file_fd.read().strip())
         return _ids
 
@@ -687,18 +764,24 @@ def _get_clear_ids(self):
                    doc="Get the passthru namespace clear_ids attribute.")
 
     def set_clear_ids(self, clear):
+        '''
+        Set the passthru namespace clear_ids attribute.
+        '''
         self._check_self()
-        path = "%s/clear_ids" % self.path
+        path = f"{self.path}/clear_ids"
         if os.path.isfile(path):
-            with open(path, 'w') as file_fd:
+            with open(path, 'w', encoding="utf-8") as file_fd:
                 file_fd.write(str(clear))
 
     def _get_admin_timeout(self):
+        '''
+        Get the passthru admin command timeout.
+        '''
         self._check_self()
-        path = "%s/admin_timeout" % self.path
+        path = f"{self.path}/admin_timeout"
         _timeout = 0
         if os.path.isfile(path):
-            with open(path, 'r') as file_fd:
+            with open(path, 'r', encoding="utf-8") as file_fd:
                 _timeout = int(file_fd.read().strip())
         return _timeout
 
@@ -706,18 +789,24 @@ def _get_admin_timeout(self):
                              doc="Get the passthru admin command timeout.")
 
     def set_admin_timeout(self, timeout):
+        '''
+        Set the passthru admin command timeout.
+        '''
         self._check_self()
-        path = "%s/admin_timeout" % self.path
+        path = f"{self.path}/admin_timeout"
         if os.path.isfile(path):
-            with open(path, 'w') as file_fd:
+            with open(path, 'w', encoding="utf-8") as file_fd:
                 file_fd.write(str(timeout))
 
     def _get_io_timeout(self):
+        '''
+        Get the passthru IO command timeout.
+        '''
         self._check_self()
-        path = "%s/io_timeout" % self.path
+        path = f"{self.path}/io_timeout"
         _timeout = 0
         if os.path.isfile(path):
-            with open(path, 'r') as file_fd:
+            with open(path, 'r', encoding="utf-8") as file_fd:
                 _timeout = int(file_fd.read().strip())
         return _timeout
 
@@ -725,18 +814,24 @@ def _get_io_timeout(self):
                           doc="Get the passthru IO command timeout.")
 
     def set_io_timeout(self, timeout):
+        '''
+        Set the passthru IO command timeout.
+        '''
         self._check_self()
-        path = "%s/io_timeout" % self.path
+        path = f"{self.path}/io_timeout"
         if os.path.isfile(path):
-            with open(path, 'w') as file_fd:
+            with open(path, 'w', encoding="utf-8") as file_fd:
                 file_fd.write(str(timeout))
 
     @classmethod
     def setup(cls, subsys, p, err_func):
+        '''
+        Set up a Passthru object based upon p dict, from saved config.
+        '''
         try:
             pt = Passthru(subsys)
         except CFSError as e:
-            err_func("Could not create Passthru object: %s" % e)
+            err_func(f"Could not create Passthru object: {e}")
             return
         pt._setup_attrs(p, err_func)
         if 'clear_ids' in p:
@@ -747,7 +842,10 @@ def setup(cls, subsys, p, err_func):
             pt.set_io_timeout(int(p['io_timeout']))
 
     def dump(self):
-        d = super(Passthru, self).dump()
+        '''
+        Returns a dict with the config of the object.
+        '''
+        d = super().dump()
         d['clear_ids'] = self.ids
         d['admin_timeout'] = self.admin_timeout
         d['io_timeout'] = self.io_timeout
@@ -762,24 +860,30 @@ class Port(CFSNode):
     MAX_PORTID = 8192
 
     def __repr__(self):
-        return "<Port %d>" % self.portid
+        return f"<Port {self.portid}>"
 
     def __init__(self, portid, mode='any'):
-        super(Port, self).__init__()
+        super().__init__()
 
         self.attr_groups = ['addr', 'param']
         self._portid = int(portid)
-        self._path = "%s/ports/%d" % (self.configfs_dir, self._portid)
+        self._path = f"{self.configfs_dir}/ports/{self._portid}"
         self._create_in_cfs(mode)
 
     def _get_portid(self):
+        '''
+        Returns the port ID.
+        '''
         return self._portid
 
     portid = property(_get_portid, doc="Get the Port ID as an int.")
 
     def _list_subsystems(self):
+        '''
+        Lists the subsystems of the port.
+        '''
         return [os.path.basename(name)
-                for name in os.listdir("%s/subsystems/" % self._path)]
+                for name in os.listdir(f"{self._path}/subsystems/")]
 
     subsystems = property(_list_subsystems,
                           doc="Get the list of Subsystem for this Port.")
@@ -789,19 +893,19 @@ def add_subsystem(self, nqn):
         Enable access to the Subsystem identified by I{nqn} through this Port.
         '''
         try:
-            os.symlink("%s/subsystems/%s" % (self.configfs_dir, nqn),
-                       "%s/subsystems/%s" % (self._path, nqn))
-        except Exception as e:
-            raise CFSError("Could not symlink %s in configFS: %s" % (nqn, e))
+            os.symlink(f"{self.configfs_dir}/subsystems/{nqn}",
+                       f"{self._path}/subsystems/{nqn}")
+        except OSError as e:
+            raise CFSError(f"Could not symlink {nqn} in configFS: {e}") from e
 
     def remove_subsystem(self, nqn):
         '''
         Disable access to the Subsystem identified by I{nqn} through this Port.
         '''
         try:
-            os.unlink("%s/subsystems/%s" % (self._path, nqn))
-        except Exception as e:
-            raise CFSError("Could not unlink %s in configFS: %s" % (nqn, e))
+            os.unlink(f"{self._path}/subsystems/{nqn}")
+        except OSError as e:
+            raise CFSError(f"Could not unlink {nqn} in configFS: {e}") from e
 
     def delete(self):
         '''
@@ -814,27 +918,33 @@ def delete(self):
             a.delete()
         for r in self.referrals:
             r.delete()
-        super(Port, self).delete()
+        super().delete()
 
     def _list_referrals(self):
+        '''
+        Lists the referrals of the port.
+        '''
         self._check_self()
-        for d in os.listdir("%s/referrals/" % self._path):
+        for d in os.listdir(f"{self._path}/referrals/"):
             yield Referral(self, d, 'lookup')
 
     referrals = property(_list_referrals,
                          doc="Get the list of Referrals for this Port.")
 
     def _list_ana_groups(self):
+        '''
+        Lists the ANA groups of the port.
+        '''
         self._check_self()
-        if os.path.isdir("%s/ana_groups/" % self._path):
-            for d in os.listdir("%s/ana_groups/" % self._path):
+        if os.path.isdir(f"{self._path}/ana_groups/"):
+            for d in os.listdir(f"{self._path}/ana_groups/"):
                 yield ANAGroup(self, int(d), 'lookup')
 
     ana_groups = property(_list_ana_groups,
                           doc="Get the list of ANA Groups for this Port.")
 
     @classmethod
-    def setup(cls, root, n, err_func):
+    def setup(cls, n, err_func):
         '''
         Set up a Port object based upon n dict, from saved config.
         Guard against missing or bad dict items, but keep going.
@@ -848,7 +958,7 @@ def setup(cls, root, n, err_func):
         try:
             port = Port(n['portid'])
         except CFSError as e:
-            err_func("Could not create Port object: %s" % e)
+            err_func(f"Could not create Port object: {e}")
             return
 
         port._setup_attrs(n, err_func)
@@ -860,7 +970,10 @@ def setup(cls, root, n, err_func):
             Referral.setup(port, r, err_func)
 
     def dump(self):
-        d = super(Port, self).dump()
+        '''
+        Returns a dict with the config of the object.
+        '''
+        d = super().dump()
         d['portid'] = self.portid
         d['subsystems'] = self.subsystems
         d['ana_groups'] = [a.dump() for a in self.ana_groups]
@@ -874,10 +987,10 @@ class Referral(CFSNode):
     '''
 
     def __repr__(self):
-        return "<Referral %d>" % self.name
+        return f"<Referral {self.name}>"
 
     def __init__(self, port, name, mode='any'):
-        super(Referral, self).__init__()
+        super().__init__()
 
         if not isinstance(port, Port):
             raise CFSError("Invalid parent class")
@@ -885,10 +998,13 @@ def __init__(self, port, name, mode='any'):
         self.attr_groups = ['addr']
         self.port = port
         self._name = name
-        self._path = "%s/referrals/%s" % (self.port.path, self._name)
+        self._path = f"{self.port.path}/referrals/{self._name}"
         self._create_in_cfs(mode)
 
     def _get_name(self):
+        '''
+        Returns the name of the referral.
+        '''
         return self._name
 
     name = property(_get_name, doc="Get the Referral name.")
@@ -908,13 +1024,16 @@ def setup(cls, port, n, err_func):
         try:
             r = Referral(port, n['name'])
         except CFSError as e:
-            err_func("Could not create Referral object: %s" % e)
+            err_func(f"Could not create Referral object: {e}")
             return
 
         r._setup_attrs(n, err_func)
 
     def dump(self):
-        d = super(Referral, self).dump()
+        '''
+        Returns a dict with the config of the object.
+        '''
+        d = super().dump()
         d['name'] = self.name
         return d
 
@@ -927,12 +1046,12 @@ class ANAGroup(CFSNode):
     MAX_GRPID = 1024
 
     def __repr__(self):
-        return "<ANA Group %d>" % self.grpid
+        return f"<ANA Group {self.grpid}>"
 
     def __init__(self, port, grpid, mode='any'):
-        super(ANAGroup, self).__init__()
+        super().__init__()
 
-        if not os.path.isdir("%s/ana_groups" % port.path):
+        if not os.path.isdir(f"{port.path}/ana_groups"):
             raise CFSError("ANA not supported")
 
         if grpid is None:
@@ -945,20 +1064,22 @@ def __init__(self, port, grpid, mode='any'):
                     grpid = index
                     break
             if grpid is None:
-                raise CFSError("All ANA Group IDs 1-%d in use" % self.MAX_GRPID)
+                raise CFSError(f"All ANA Group IDs 1-{self.MAX_GRPID} in use")
         else:
             grpid = int(grpid)
             if grpid < 1 or grpid > self.MAX_GRPID:
-                raise CFSError("GRPID %d must be 1 to %d"
-                               % (grpid, self.MAX_GRPID))
+                raise CFSError(f"GRPID {grpid} must be 1 to {self.MAX_GRPID}")
 
         self.attr_groups = ['ana']
         self._port = port
         self._grpid = grpid
-        self._path = "%s/ana_groups/%d" % (self._port.path, self.grpid)
+        self._path = f"{self._port.path}/ana_groups/{self.grpid}"
         self._create_in_cfs(mode)
 
     def _get_grpid(self):
+        '''
+        Returns the ANA group ID.
+        '''
         return self._grpid
 
     grpid = property(_get_grpid, doc="Get the ANA Group ID.")
@@ -978,18 +1099,24 @@ def setup(cls, port, n, err_func):
         try:
             a = ANAGroup(port, n['grpid'])
         except CFSError as e:
-            err_func("Could not create ANA Group object: %s" % e)
+            err_func(f"Could not create ANA Group object: {e}")
             return
 
         a._setup_attrs(n, err_func)
 
     def delete(self):
+        '''
+        Deletes the ANA group.
+        '''
         # ANA Group 1 is automatically created/deleted
         if self.grpid != 1:
-            super(ANAGroup, self).delete()
+            super().delete()
 
     def dump(self):
-        d = super(ANAGroup, self).dump()
+        '''
+        Returns a dict with the config of the object.
+        '''
+        d = super().dump()
         d['grpid'] = self.grpid
         return d
 
@@ -1001,7 +1128,7 @@ class Host(CFSNode):
     '''
 
     def __repr__(self):
-        return "<Host %s>" % self.nqn
+        return f"<Host {self.nqn}>"
 
     def __init__(self, nqn, mode='any'):
         '''
@@ -1015,10 +1142,10 @@ def __init__(self, nqn, mode='any'):
         @type mode:string
         @return: A Host object.
         '''
-        super(Host, self).__init__()
+        super().__init__()
 
         self.nqn = nqn
-        self._path = "%s/hosts/%s" % (self.configfs_dir, nqn)
+        self._path = f"{self.configfs_dir}/hosts/{nqn}"
         self._create_in_cfs(mode)
 
     @classmethod
@@ -1036,19 +1163,23 @@ def setup(cls, t, err_func):
         try:
             Host(t['nqn'])
         except CFSError as e:
-            err_func("Could not create Host object: %s" % e)
+            err_func(f"Could not create Host object: {e}")
             return
 
     def dump(self):
-        d = super(Host, self).dump()
+        '''
+        Returns a dict with the config of the object.
+        '''
+        d = super().dump()
         d['nqn'] = self.nqn
         return d
 
 
 def _test():
-    from doctest import testmod
     testmod()
 
 
 if __name__ == "__main__":
     _test()
+
+# pylint: disable=too-many-lines
diff --git a/nvmet/test_nvmet.py b/nvmet/test_nvmet.py
index ecbbf90..5c5e781 100644
--- a/nvmet/test_nvmet.py
+++ b/nvmet/test_nvmet.py
@@ -1,10 +1,13 @@
+"""
+Tests for the nvmet API.
+"""
 
 import os
 import random
 import stat
 import string
 import unittest
-import nvmet.nvme as nvme
+from nvmet import nvme
 
 # Default test devices are ram disks, but allow user to specify different
 # block devices or files.
@@ -13,17 +16,26 @@
 
 
 def test_devices_present():
+    '''
+    Check if the test devices are present.
+    '''
     return len([x for x in NVMET_TEST_DEVICES
                 if os.path.exists(x) and
                 (stat.S_ISBLK(os.stat(x).st_mode) or os.path.isfile(x))]) >= 2
 
 
 class TestNvmet(unittest.TestCase):
+    '''
+    Tests for the nvmet API.
+    '''
     def test_subsystem(self):
+        '''
+        Test Subsystem creation and deletion.
+        '''
         root = nvme.Root()
         root.clear_existing()
-        for s in root.subsystems:
-            self.assertTrue(False, 'Found Subsystem after clear')
+        for _ in root.subsystems:
+            self.fail('Found Subsystem after clear')
 
         # create mode
         s1 = nvme.Subsystem(nqn='testnqn1', mode='create')
@@ -64,12 +76,15 @@ def test_subsystem(self):
         self.assertEqual(len(list(root.subsystems)), 0)
 
     def test_namespace(self):
+        '''
+        Test Namespace creation and deletion.
+        '''
         root = nvme.Root()
         root.clear_existing()
 
         s = nvme.Subsystem(nqn='testnqn', mode='create')
-        for n in s.namespaces:
-            self.assertTrue(False, 'Found Namespace in new Subsystem')
+        for _ in s.namespaces:
+            self.fail('Found Namespace in new Subsystem')
 
         # create mode
         n1 = nvme.Namespace(s, nsid=3, mode='create')
@@ -115,9 +130,12 @@ def test_namespace(self):
         self.assertEqual(len(list(s.namespaces)), 0)
 
     @unittest.skipUnless(test_devices_present(),
-                         "Devices %s not available or suitable"
-                         % ','.join(NVMET_TEST_DEVICES))
+                         f"Devices {','.join(NVMET_TEST_DEVICES)} "
+                         f"not available or suitable")
     def test_namespace_attrs(self):
+        '''
+        Test Namespace attributes.
+        '''
         root = nvme.Root()
         root.clear_existing()
 
@@ -154,6 +172,9 @@ def test_namespace_attrs(self):
         n.delete()
 
     def test_recursive_delete(self):
+        '''
+        Test recursive deletion of a Subsystem.
+        '''
         root = nvme.Root()
         root.clear_existing()
 
@@ -165,10 +186,13 @@ def test_recursive_delete(self):
         self.assertEqual(len(list(root.subsystems)), 0)
 
     def test_port(self):
+        '''
+        Test Port creation and deletion.
+        '''
         root = nvme.Root()
         root.clear_existing()
-        for p in root.ports:
-            self.assertTrue(False, 'Found Port after clear')
+        for _ in root.ports:
+            self.fail('Found Port after clear')
 
         # create mode
         p1 = nvme.Port(portid=0, mode='create')
@@ -201,6 +225,9 @@ def test_port(self):
         self.assertEqual(len(list(root.ports)), 0)
 
     def test_loop_port(self):
+        '''
+        Test loop port functionality.
+        '''
         root = nvme.Root()
         root.clear_existing()
 
@@ -254,10 +281,13 @@ def test_loop_port(self):
         p.delete()
 
     def test_host(self):
+        '''
+        Test Host creation and deletion.
+        '''
         root = nvme.Root()
         root.clear_existing()
-        for p in root.hosts:
-            self.assertTrue(False, 'Found Host after clear')
+        for _ in root.hosts:
+            self.fail('Found Host after clear')
 
         # create mode
         h1 = nvme.Host(nqn='foo', mode='create')
@@ -290,6 +320,9 @@ def test_host(self):
         self.assertEqual(len(list(root.hosts)), 0)
 
     def test_referral(self):
+        '''
+        Test Referral creation and deletion.
+        '''
         root = nvme.Root()
         root.clear_existing()
 
@@ -373,6 +406,9 @@ def test_referral(self):
         self.assertEqual(len(list(p.referrals)), 0)
 
     def test_allowed_hosts(self):
+        '''
+        Test allowed hosts functionality.
+        '''
         nvme.Root()
 
         nvme.Host(nqn='hostnqn', mode='create')
@@ -398,6 +434,9 @@ def test_allowed_hosts(self):
         self.assertRaises(nvme.CFSError, s.remove_allowed_host, 'foobar')
 
     def test_invalid_input(self):
+        '''
+        Test invalid input to the API.
+        '''
         root = nvme.Root()
         root.clear_existing()
 
@@ -420,9 +459,12 @@ def test_invalid_input(self):
                           portid=1 << 17, mode='create')
 
     @unittest.skipUnless(test_devices_present(),
-                         "Devices %s not available or suitable" % ','.join(
-                             NVMET_TEST_DEVICES))
+                         f"Devices {','.join(NVMET_TEST_DEVICES)} not "
+                         f"available or suitable")
     def test_save_restore(self):
+        '''
+        Test save and restore functionality.
+        '''
         root = nvme.Root()
         root.clear_existing()
 
diff --git a/nvmetcli b/nvmetcli
index bec4897..f39e8af 100755
--- a/nvmetcli
+++ b/nvmetcli
@@ -22,18 +22,24 @@ from __future__ import print_function
 
 import os
 import sys
-import configshell
-import nvmet as nvme
 import errno
 from string import hexdigits
 import uuid
+import configshell
+import nvmet as nvme
 
 
-def ngiud_set(nguid):
+def nguid_set(nguid):
+    '''
+    Check if the nguid is set.
+    '''
     return any(c in hexdigits and c != '0' for c in nguid)
 
 
 class UINode(configshell.ConfigNode):
+    '''
+    A node in the UI.
+    '''
     def __init__(self, name, parent=None, cfnode=None, shell=None):
         configshell.ConfigNode.__init__(self, name, parent, shell)
         self.cfnode = cfnode
@@ -44,10 +50,10 @@ class UINode(configshell.ConfigNode):
         self.refresh()
 
     def _init_group(self, group):
-        setattr(self.__class__, "ui_getgroup_%s" % group,
+        setattr(self.__class__, f"ui_getgroup_{group}",
                 lambda self, attr:
                     self.cfnode.get_attr(group, attr))
-        setattr(self.__class__, "ui_setgroup_%s" % group,
+        setattr(self.__class__, f"ui_setgroup_{group}",
                 lambda self, attr, value:
                     self.cfnode.set_attr(group, attr, value))
 
@@ -56,14 +62,20 @@ class UINode(configshell.ConfigNode):
         for attr in attrs:
             writable = attr not in attrs_ro
 
-            name = "ui_desc_%s" % group
+            name = f"ui_desc_{group}"
             t, d = getattr(self.__class__, name, {}).get(attr, ('string', ''))
             self.define_config_group_param(group, attr, t, d, writable)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
 
     def status(self):
+        '''
+        Displays the current node's status summary.
+        '''
         return "None"
 
     def ui_command_refresh(self):
@@ -80,7 +92,7 @@ class UINode(configshell.ConfigNode):
         ========
         B{ls}
         '''
-        self.shell.log.info("Status for %s: %s" % (self.path, self.status()))
+        self.shell.log.info(f"Status for {self.path}: {self.status()}")
 
     def ui_command_saveconfig(self, savefile=None):
         '''
@@ -94,6 +106,9 @@ class UINode(configshell.ConfigNode):
 
 
 class UIRootNode(UINode):
+    '''
+    The root node of the UI.
+    '''
     ui_desc_discovery = {
         'nqn': ('string', 'Discovery NQN'),
     }
@@ -103,14 +118,20 @@ class UIRootNode(UINode):
                         shell=shell)
 
     def summary(self):
+        '''
+        Returns a summary of the root node.
+        '''
         info = []
         try:
-            info.append("discovery=" + self.cfnode.get_attr("discovery", "nqn"))
+            info.append(f"discovery={self.cfnode.get_attr('discovery', 'nqn')}")
         except nvme.nvme.CFSError:
             pass
         return (", ".join(info), True)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         UISubsystemsNode(self)
         UIPortsNode(self)
@@ -122,18 +143,23 @@ class UIRootNode(UINode):
         '''
         errors = self.cfnode.restore_from_file(savefile, clear_existing)
         self.refresh()
-
         if errors:
             raise configshell.ExecutionError(
-                "Configuration restored, %d errors:\n%s" %
-                (len(errors), "\n".join(errors)))
+                "Configuration restored, {} errors:\n{}".format(
+                    len(errors), "\n".join(errors)))
 
 
 class UISubsystemsNode(UINode):
+    '''
+    A node in the UI representing the subsystems.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'subsystems', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for subsys in self.parent.cfnode.subsystems:
             UISubsystemNode(self, subsys)
@@ -165,6 +191,9 @@ class UISubsystemsNode(UINode):
 
 
 class UISubsystemNode(UINode):
+    '''
+    A node in the UI representing a subsystem.
+    '''
     ui_desc_attr = {
         'allow_any_host': ('string', 'Allow access by any host if set to 1'),
         'serial': ('string', 'Export serial number to hosts'),
@@ -175,6 +204,9 @@ class UISubsystemNode(UINode):
         UINode.__init__(self, cfnode.nqn, parent, cfnode)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         UINamespacesNode(self)
         UIAllowedHostsNode(self)
@@ -182,15 +214,21 @@ class UISubsystemNode(UINode):
             UIPassthruNode(self)
 
     def summary(self):
+        '''
+        Returns a summary of the subsystem.
+        '''
         info = []
-        info.append("version=" + self.cfnode.get_attr("attr", "version"))
-        info.append("allow_any=" +
-                    self.cfnode.get_attr("attr", "allow_any_host"))
-        info.append("serial=" + self.cfnode.get_attr("attr", "serial"))
+        info.append(f"version={self.cfnode.get_attr('attr', 'version')}")
+        info.append(f"allow_any="
+                    f"{self.cfnode.get_attr('attr', 'allow_any_host')}")
+        info.append(f"serial={self.cfnode.get_attr('attr', 'serial')}")
         return (", ".join(info), True)
 
 
 class UIPassthruNode(UINode):
+    '''
+    A node in the UI representing a passthru.
+    '''
     ui_desc_device = {
         'path': ('string', 'Passthru device path')
     }
@@ -200,40 +238,49 @@ class UIPassthruNode(UINode):
         UINode.__init__(self, 'passthru', parent, passthru)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
 
     def ui_command_enable(self):
+        '''
+        Enables the passthru.
+        '''
         if self.cfnode.get_enable():
             self.shell.log.info("The passthru is already enabled.")
         else:
             try:
                 self.cfnode.set_enable(1)
                 self.shell.log.info("The passthru has been enabled.")
-            except Exception:
+            except Exception as exc:
                 raise configshell.ExecutionError(
-                    "The passthru could not be enabled.")
+                    "The passthru could not be enabled.") from exc
 
     def ui_command_disable(self):
+        '''
+        Disables the passthru.
+        '''
         if not self.cfnode.get_enable():
             self.shell.log.info("The passthru is already disabled.")
         else:
             try:
                 self.cfnode.set_enable(0)
                 self.shell.log.info("The passthru has been disabled.")
-            except Exception:
+            except Exception as exc:
                 raise configshell.ExecutionError(
-                    "The passthru could not be disabled.")
+                    "The passthru could not be disabled.") from exc
 
-    def ui_command_clear_ids(self, clear):
+    def ui_command_clear_ids(self, clear_id):
         '''
-        If I{clear} is set to non-zero then clears the passthru namespace
+        If I{clear_id} is set to non-zero then clears the passthru namespace
         unique identifiers EUI/GUID/UUID.
         '''
         try:
-            self.cfnode.set_clear_ids(clear)
-        except Exception:
+            self.cfnode.set_clear_ids(clear_id)
+        except Exception as exc:
             raise configshell.ExecutionError(
-                "Failed to set clear_ids for this passthru target.")
+                "Failed to set clear_ids for this passthru target.") from exc
 
     def ui_command_admin_timeout(self, timeout):
         '''
@@ -241,9 +288,9 @@ class UIPassthruNode(UINode):
         '''
         try:
             self.cfnode.set_admin_timeout(timeout)
-        except Exception:
+        except Exception as exc:
             raise configshell.ExecutionError(
-                "Failed to set the admin passthru command timeout.")
+                "Failed to set the admin passthru command timeout.") from exc
 
     def ui_command_io_timeout(self, timeout):
         '''
@@ -251,9 +298,9 @@ class UIPassthruNode(UINode):
         '''
         try:
             self.cfnode.set_io_timeout(timeout)
-        except Exception:
+        except Exception as exc:
             raise configshell.ExecutionError(
-                "Failed to set the IO passthru command timeout.")
+                "Failed to set the IO passthru command timeout.") from exc
 
     def summary(self):
         info = []
@@ -269,10 +316,16 @@ class UIPassthruNode(UINode):
 
 
 class UINamespacesNode(UINode):
+    '''
+    A node in the UI representing the namespaces.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'namespaces', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for ns in self.parent.cfnode.namespaces:
             UINamespaceNode(self, ns)
@@ -304,6 +357,9 @@ class UINamespacesNode(UINode):
 
 
 class UINamespaceNode(UINode):
+    '''
+    A node in the UI representing a namespace.
+    '''
     ui_desc_device = {
         'path': ('string', 'Backing device path.'),
         'nguid': ('string', 'Namspace Global Unique Identifier.'),
@@ -314,6 +370,9 @@ class UINamespaceNode(UINode):
         UINode.__init__(self, str(cfnode.nsid), parent, cfnode)
 
     def status(self):
+        '''
+        Returns the status of the namespace.
+        '''
         if self.cfnode.get_enable():
             return "enabled"
         return "disabled"
@@ -332,9 +391,9 @@ class UINamespaceNode(UINode):
             try:
                 self.cfnode.set_enable(1)
                 self.shell.log.info("The Namespace has been enabled.")
-            except Exception:
+            except Exception as exc:
                 raise configshell.ExecutionError(
-                    "The Namespace could not be enabled.")
+                    "The Namespace could not be enabled.") from exc
 
     def ui_command_disable(self):
         '''
@@ -350,9 +409,9 @@ class UINamespaceNode(UINode):
             try:
                 self.cfnode.set_enable(0)
                 self.shell.log.info("The Namespace has been disabled.")
-            except Exception:
+            except Exception as exc:
                 raise configshell.ExecutionError(
-                    "The Namespace could not be disabled.")
+                    "The Namespace could not be enabled.") from exc
 
     def ui_command_grpid(self, grpid):
         '''
@@ -360,9 +419,9 @@ class UINamespaceNode(UINode):
         '''
         try:
             self.cfnode.set_grpid(grpid)
-        except Exception:
+        except Exception as exc:
             raise configshell.ExecutionError(
-                "Failed to set ANA Group ID for this Namespace.")
+                "Failed to set ANA Group ID for this Namespace.") from exc
 
     def summary(self):
         info = []
@@ -371,8 +430,8 @@ class UINamespaceNode(UINode):
         if uuid.UUID(ns_uuid).int != 0:
             info.append("uuid=" + str(ns_uuid))
         ns_nguid = self.cfnode.get_attr("device", "nguid")
-        if ngiud_set(ns_nguid):
-            info.append("nguid=" + ns_nguid)
+        if nguid_set(ns_nguid):
+            info.append(f"nguid={ns_nguid}")
         if self.cfnode.grpid != 0:
             info.append("grpid=" + str(self.cfnode.grpid))
         try:
@@ -386,10 +445,16 @@ class UINamespaceNode(UINode):
 
 
 class UIAllowedHostsNode(UINode):
+    '''
+    A node in the UI representing the allowed hosts.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'allowed_hosts', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for host in self.parent.cfnode.allowed_hosts:
             UIAllowedHostNode(self, host)
@@ -405,16 +470,18 @@ class UIAllowedHostsNode(UINode):
         self.parent.cfnode.add_allowed_host(nqn)
         UIAllowedHostNode(self, nqn)
 
-    def ui_complete_create(self, parameters, text, current_param):
+    def ui_complete_create(self, _parameters, _text, current_param):
+        '''
+        Completes the create command.
+        '''
         completions = []
         if current_param == 'nqn':
             for host in self.get_node('/hosts').children:
                 completions.append(host.cfnode.nqn)
 
         if len(completions) == 1:
-            return [completions[0] + ' ']
-        else:
-            return completions
+            return [f"{completions[0]} "]
+        return completions
 
     def ui_command_delete(self, nqn):
         '''
@@ -428,28 +495,39 @@ class UIAllowedHostsNode(UINode):
         self.parent.cfnode.remove_allowed_host(nqn)
         self.refresh()
 
-    def ui_complete_delete(self, parameters, text, current_param):
+    def ui_complete_delete(self, _parameters, _text, current_param):
+        '''
+        Completes the delete command.
+        '''
         completions = []
         if current_param == 'nqn':
             for nqn in self.parent.cfnode.allowed_hosts:
                 completions.append(nqn)
 
         if len(completions) == 1:
-            return [completions[0] + ' ']
-        else:
-            return completions
+            return [f"{completions[0]} "]
+        return completions
 
 
 class UIAllowedHostNode(UINode):
+    '''
+    A node in the UI representing an allowed host.
+    '''
     def __init__(self, parent, nqn):
         UINode.__init__(self, nqn, parent)
 
 
 class UIPortsNode(UINode):
+    '''
+    A node in the UI representing the ports.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'ports', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for port in self.parent.cfnode.ports:
             UIPortNode(self, port)
@@ -480,6 +558,9 @@ class UIPortsNode(UINode):
 
 
 class UIPortNode(UINode):
+    '''
+    A node in the UI representing a port.
+    '''
     ui_desc_addr = {
         'adrfam': ('string', 'Address Family (e.g. ipv4 or fc)'),
         'treq': ('string', 'Transport Security Requirements'),
@@ -504,31 +585,38 @@ class UIPortNode(UINode):
         UIReferralsNode(self)
 
     def summary(self):
+        '''
+        Returns a summary of the port.
+        '''
         info = []
-        info.append("trtype=" + self.cfnode.get_attr("addr", "trtype"))
-        info.append("traddr=" + self.cfnode.get_attr("addr", "traddr"))
+        info.append(f"trtype={self.cfnode.get_attr('addr', 'trtype')}")
+        info.append(f"traddr={self.cfnode.get_attr('addr', 'traddr')}")
         trsvcid = self.cfnode.get_attr("addr", "trsvcid")
         if trsvcid != "none":
-            info.append("trsvcid=%s" % trsvcid)
+            info.append(f"trsvcid={trsvcid}")
 
-        '''
-        Support older target driver w/o the inline_data_size parameter
-        '''
+        # Support older target driver w/o the inline_data_size parameter
         try:
             inline_data_size = self.cfnode.get_attr("param", "inline_data_size")
-        except Exception:
+        except nvme.CFSError:
             inline_data_size = "n/a"
         if inline_data_size != "n/a":
-            info.append("inline_data_size=" + inline_data_size)
+            info.append(f"inline_data_size={inline_data_size}")
         enabled = self.cfnode.subsystems or list(self.cfnode.referrals)
         return (", ".join(info), True if enabled else 0)
 
 
 class UIPortSubsystemsNode(UINode):
+    '''
+    A node in the UI representing the port subsystems.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'subsystems', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for host in self.parent.cfnode.subsystems:
             UIPortSubsystemNode(self, host)
@@ -545,16 +633,18 @@ class UIPortSubsystemsNode(UINode):
         self.parent.cfnode.add_subsystem(nqn)
         UIPortSubsystemNode(self, nqn)
 
-    def ui_complete_create(self, parameters, text, current_param):
+    def ui_complete_create(self, _parameters, _text, current_param):
+        '''
+        Completes the create command.
+        '''
         completions = []
         if current_param == 'nqn':
             for subsys in self.get_node('/subsystems').children:
                 completions.append(subsys.cfnode.nqn)
 
         if len(completions) == 1:
-            return [completions[0] + ' ']
-        else:
-            return completions
+            return [f"{completions[0]} "]
+        return completions
 
     def ui_command_delete(self, nqn):
         '''
@@ -568,28 +658,39 @@ class UIPortSubsystemsNode(UINode):
         self.parent.cfnode.remove_subsystem(nqn)
         self.refresh()
 
-    def ui_complete_delete(self, parameters, text, current_param):
+    def ui_complete_delete(self, _parameters, _text, current_param):
+        '''
+        Completes the delete command.
+        '''
         completions = []
         if current_param == 'nqn':
             for nqn in self.parent.cfnode.subsystems:
                 completions.append(nqn)
 
         if len(completions) == 1:
-            return [completions[0] + ' ']
-        else:
-            return completions
+            return [f"{completions[0]} "]
+        return completions
 
 
 class UIPortSubsystemNode(UINode):
+    '''
+    A node in the UI representing a port subsystem.
+    '''
     def __init__(self, parent, nqn):
         UINode.__init__(self, nqn, parent)
 
 
 class UIReferralsNode(UINode):
+    '''
+    A node in the UI representing the referrals.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'referrals', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for r in self.parent.cfnode.referrals:
             UIReferralNode(self, r)
@@ -619,6 +720,9 @@ class UIReferralsNode(UINode):
 
 
 class UIReferralNode(UINode):
+    '''
+    A node in the UI representing a referral.
+    '''
     ui_desc_addr = {
         'adrfam': ('string', 'Address Family (e.g. ipv4 or fc)'),
         'treq': ('string', 'Transport Security Requirements'),
@@ -633,6 +737,9 @@ class UIReferralNode(UINode):
         UINode.__init__(self, cfnode.name, parent, cfnode)
 
     def status(self):
+        '''
+        Returns the status of the referral.
+        '''
         if self.cfnode.get_enable():
             return "enabled"
         return "disabled"
@@ -651,9 +758,9 @@ class UIReferralNode(UINode):
             try:
                 self.cfnode.set_enable(1)
                 self.shell.log.info("The Referral has been enabled.")
-            except Exception:
+            except Exception as exc:
                 raise configshell.ExecutionError(
-                    "The Referral could not be enabled.")
+                    "The Referral could not be enabled.") from exc
 
     def ui_command_disable(self):
         '''
@@ -669,16 +776,22 @@ class UIReferralNode(UINode):
             try:
                 self.cfnode.set_enable(0)
                 self.shell.log.info("The Referral has been disabled.")
-            except Exception:
+            except Exception as exc:
                 raise configshell.ExecutionError(
-                    "The Referral could not be disabled.")
+                    "The Referral could not be enabled.") from exc
 
 
 class UIANAGroupsNode(UINode):
+    '''
+    A node in the UI representing the ANA groups.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'ana_groups', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for a in self.parent.cfnode.ana_groups:
             UIANAGroupNode(self, a)
@@ -708,6 +821,9 @@ class UIANAGroupsNode(UINode):
 
 
 class UIANAGroupNode(UINode):
+    '''
+    A node in the UI representing an ANA group.
+    '''
     ui_desc_ana = {
         'state': ('string', 'ANA state'),
     }
@@ -716,16 +832,25 @@ class UIANAGroupNode(UINode):
         UINode.__init__(self, str(cfnode.grpid), parent, cfnode)
 
     def summary(self):
+        '''
+        Returns a summary of the ANA group.
+        '''
         info = []
-        info.append("state=" + self.cfnode.get_attr("ana", "state"))
+        info.append(f"state={self.cfnode.get_attr('ana', 'state')}")
         return (", ".join(info), True)
 
 
 class UIHostsNode(UINode):
+    '''
+    A node in the UI representing the hosts.
+    '''
     def __init__(self, parent):
         UINode.__init__(self, 'hosts', parent)
 
     def refresh(self):
+        '''
+        Refreshes and updates the objects tree from the current path.
+        '''
         self._children = set([])
         for host in self.parent.cfnode.hosts:
             UIHostNode(self, host)
@@ -756,24 +881,36 @@ class UIHostsNode(UINode):
 
 
 class UIHostNode(UINode):
+    '''
+    A node in the UI representing a host.
+    '''
     def __init__(self, parent, cfnode):
         UINode.__init__(self, cfnode.nqn, parent, cfnode)
 
 
 def usage():
-    print("syntax: %s save [file_to_save_to]" % sys.argv[0])
-    print("        %s restore [file_to_restore_from]" % sys.argv[0])
-    print("        %s clear" % sys.argv[0])
-    print("        %s --help  (Print this information)" % sys.argv[0])
-    print("        %s <CMD>   (Run shell command and exit)" % sys.argv[0])
+    '''
+    Prints the usage message.
+    '''
+    print(f"syntax: {sys.argv[0]} save [file_to_save_to]")
+    print(f"        {sys.argv[0]} restore [file_to_restore_from]")
+    print(f"        {sys.argv[0]} clear")
+    print(f"        {sys.argv[0]} --help  (Print this information)")
+    print(f"        {sys.argv[0]} <CMD>   (Run shell command and exit)")
     sys.exit(-1)
 
 
 def save(to_file):
+    '''
+    Saves the configuration to a file.
+    '''
     nvme.Root().save_to_file(to_file)
 
 
 def restore(from_file):
+    '''
+    Restores the configuration from a file.
+    '''
     errors = None
 
     try:
@@ -784,11 +921,11 @@ def restore(from_file):
 
         if e.errno == errno.ENOENT:
             # Not an error if the restore file is not present
-            print("No saved config file at %s, ok, exiting" % from_file)
+            print(f"No saved config file at {from_file}, ok, exiting")
             sys.exit(0)
         else:
-            print("Error processing config file at %s, error %s, exiting" %
-                  (from_file, str(e)))
+            print(f"Error processing config file at {from_file}, error {e}"
+                  f", exiting")
             sys.exit(1)
 
     # These errors are non-fatal
@@ -798,54 +935,60 @@ def restore(from_file):
     sys.exit(0)
 
 
-def clear(unused):
+def clear(_unused):
+    '''
+    Clears the configuration.
+    '''
     nvme.Root().clear_existing()
 
 
 def execute_cmd(cmd):
+    '''
+    Executes a command in the shell.
+    '''
     shell = configshell.ConfigShell('~/.nvmetcli')
     UIRootNode(shell)
     shell.run_cmdline(cmd)
     sys.exit(0)
 
 
-funcs = dict(save=save, restore=restore, clear=clear)
+funcs = {'save': save, 'restore': restore, 'clear': clear}
 
 
 def main():
+    '''
+    The main function.
+    '''
     if os.geteuid() != 0:
-        print("%s: must run as root." % sys.argv[0], file=sys.stderr)
+        print(f"{sys.argv[0]}: must run as root.", file=sys.stderr)
         sys.exit(-1)
 
     if len(sys.argv) > 1:
         if sys.argv[1] == "--help":
             usage()
 
-        if sys.argv[1] in funcs.keys():
+        if sys.argv[1] in funcs:
             if len(sys.argv) > 3:
                 usage()
-            if len(sys.argv) == 3:
-                savefile = sys.argv[2]
-            else:
-                savefile = None
+            savefile = sys.argv[2] if len(sys.argv) == 3 else None
 
             funcs[sys.argv[1]](savefile)
             return
-        else:
-            concat_args = ' '.join(sys.argv[1:])
-            execute_cmd(concat_args)
+
+        concat_args = ' '.join(sys.argv[1:])
+        execute_cmd(concat_args)
 
     try:
         shell = configshell.ConfigShell('~/.nvmetcli')
         UIRootNode(shell)
-    except Exception as msg:
+    except (nvme.CFSError, configshell.ExecutionError) as msg:
         shell.log.error(str(msg))
         return
 
-    while not shell._exit:
+    while not shell._exit:  # pylint: disable=protected-access
         try:
             shell.run_interactive()
-        except Exception as msg:
+        except (nvme.CFSError, configshell.ExecutionError) as msg:
             shell.log.error(str(msg))