Fix various pylint violations

+ SchedUtils.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
+ VatHistory.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
+ VppCounters.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
+ Memif.py:
++ Do not use `len(SEQUENCE)` to determine if a sequence is empty
++ Either all return statements in a function should return an expression,
   or none of them should.
++ Update :return: on possible None.
+ Classify.py: Unnecessary "else" after "return"
+ ContainerUtils.py: Useless super delegation in method '__init__'
+ CpuUtils.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
+ DropRateSearch.py: Either all return statements in a function
  should return an expression, or none of them should.
+ IPv4NodeAddress.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
++ Also improve docstrings.
+ IPv4Setup.py: Useless super delegation in method '__init__'
+ IPv6Setup.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
++ Also improve docstrings.
+ IPv6Setup.py: standard import "from ipaddress import IPv6Network"
  should be placed before "from robot.api import logger"
+ MacSwap.py: Trailing newlines
+ NATUtil.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
+ NodePath.py: Unnecessary "else" after "return"
+ Tap.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
+ topology.py: Either all return statements in a function
  should return an expression, or none of them should.
+ topology.py: Unnecessary "else" after "return"
++ Do not use `len(SEQUENCE)` to determine if a sequence is empty
++ Improve docstrings
+ DUTSetup.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
++ Also do not compare int(ret_code) just to access zero-ness.
+ ssh.py: Do not use `len(SEQUENCE)` to determine if a sequence is empty
+ InterfaceUtil.py: Unnecessary "else" after "return"

Change-Id: Iba4244aa79661ee7df15fed5c7c6dbf04dfa88b2
Signed-off-by: Vratko Polak <vrpolak@cisco.com>

19 files changed, 111 insertions, 106 deletions

diff --git a/resources/libraries/python/Classify.py b/resources/libraries/python/Classify.py
index 2510da0b77..a59acad5c7 100644
--- a/resources/libraries/python/Classify.py
+++ b/resources/libraries/python/Classify.py
@@ -362,8 +362,7 @@ class Classify(object):
             )
         if session_index is not None:
             return data[0][session_index]
-        else:
-            return data[0]
+        return data[0]
 
     @staticmethod
     def vpp_log_plugin_acl_settings(node):
diff --git a/resources/libraries/python/ContainerUtils.py b/resources/libraries/python/ContainerUtils.py
index 54bbdbbc04..478a9781a0 100644
--- a/resources/libraries/python/ContainerUtils.py
+++ b/resources/libraries/python/ContainerUtils.py
@@ -479,9 +479,7 @@ class ContainerEngine(object):
 class LXC(ContainerEngine):
     """LXC implementation."""
 
-    def __init__(self):
-        """Initialize LXC object."""
-        super(LXC, self).__init__()
+    # Implicit constructor is inherited.
 
     def acquire(self, force=True):
         """Acquire a privileged system object where configuration is stored.
@@ -672,9 +670,7 @@ class LXC(ContainerEngine):
 class Docker(ContainerEngine):
     """Docker implementation."""
 
-    def __init__(self):
-        """Initialize Docker object."""
-        super(Docker, self).__init__()
+    # Implicit constructor is inherited.
 
     def acquire(self, force=True):
         """Pull an image or a repository from a registry.
diff --git a/resources/libraries/python/CpuUtils.py b/resources/libraries/python/CpuUtils.py
index 5d8b8a64a3..f4d52f8662 100644
--- a/resources/libraries/python/CpuUtils.py
+++ b/resources/libraries/python/CpuUtils.py
@@ -82,7 +82,7 @@ class CpuUtils(object):
                         ret, stderr))
             node['cpuinfo'] = list()
             for line in stdout.split("\n"):
-                if len(line) > 0 and line[0] != "#":
+                if line and line[0] != "#":
                     node['cpuinfo'].append([CpuUtils.__str2int(x) for x in
                                             line.split(",")])
 
diff --git a/resources/libraries/python/DUTSetup.py b/resources/libraries/python/DUTSetup.py
index 632e9ea073..8f9e94d560 100644
--- a/resources/libraries/python/DUTSetup.py
+++ b/resources/libraries/python/DUTSetup.py
@@ -42,7 +42,7 @@ class DUTSetup(object):
                                   'ActiveEnterTimestamp {name}` | '
                                   'awk \'{{print $2 $3}}\')"'.
                                   format(name=service))
-        if int(ret_code) != 0:
+        if int(ret_code):
             raise RuntimeError('DUT {host} failed to get logs from unit {name}'.
                                format(host=node['host'], name=service))
 
@@ -75,7 +75,7 @@ class DUTSetup(object):
         ret_code, _, _ = \
             ssh.exec_command_sudo('service {name} restart'.
                                   format(name=service), timeout=120)
-        if int(ret_code) != 0:
+        if int(ret_code):
             raise RuntimeError('DUT {host} failed to start service {name}'.
                                format(host=node['host'], name=service))
 
@@ -178,7 +178,7 @@ class DUTSetup(object):
             ssh.exec_command('sudo -Sn bash {0}/{1}/dut_setup.sh'.
                              format(Constants.REMOTE_FW_DIR,
                                     Constants.RESOURCES_LIB_SH), timeout=120)
-        if int(ret_code) != 0:
+        if int(ret_code):
             raise RuntimeError('DUT test setup script failed at node {name}'.
                                format(name=node['host']))
 
@@ -200,14 +200,14 @@ class DUTSetup(object):
             logger.trace('Try {}: Get VPP PID'.format(i))
             ret_code, stdout, stderr = ssh.exec_command('pidof vpp')
 
-            if int(ret_code) != 0:
+            if int(ret_code):
                 raise RuntimeError('Not possible to get PID of VPP process '
                                    'on node: {0}\n {1}'.
                                    format(node['host'], stdout + stderr))
 
             if len(stdout.splitlines()) == 1:
                 return int(stdout)
-            elif len(stdout.splitlines()) == 0:
+            elif not stdout.splitlines():
                 logger.debug("No VPP PID found on node {0}".
                              format(node['host']))
                 continue
@@ -274,7 +274,7 @@ class DUTSetup(object):
         # Try to read number of VFs from PCI address of QAT device
         for _ in range(3):
             ret_code, stdout, _ = ssh.exec_command(cmd)
-            if int(ret_code) == 0:
+            if not int(ret_code):
                 try:
                     sriov_numvfs = int(stdout)
                 except ValueError:
@@ -328,7 +328,7 @@ class DUTSetup(object):
                 format(numvfs, cryptodev.replace(':', r'\:'), timeout=180)
             ret_code, _, _ = ssh.exec_command_sudo("sh -c '{0}'".format(cmd))
 
-            if int(ret_code) != 0:
+            if int(ret_code):
                 raise RuntimeError('Failed to initialize {0} VFs on QAT device '
                                    ' on host {1}'.format(numvfs, node['host']))
 
@@ -351,7 +351,7 @@ class DUTSetup(object):
             "sh -c 'echo {0} | tee /sys/bus/pci/devices/{1}/driver/unbind'"
             .format(pci_addr, pci_addr.replace(':', r'\:')), timeout=180)
 
-        if int(ret_code) != 0:
+        if int(ret_code):
             raise RuntimeError('Failed to unbind PCI device {0} from driver on '
                                'host {1}'.format(pci_addr, node['host']))
 
@@ -376,7 +376,7 @@ class DUTSetup(object):
             "sh -c 'echo {0} | tee /sys/bus/pci/drivers/{1}/bind'".format(
                 pci_addr, driver), timeout=180)
 
-        if int(ret_code) != 0:
+        if int(ret_code):
             raise RuntimeError('Failed to bind PCI device {0} to {1} driver on '
                                'host {2}'.format(pci_addr, driver,
                                                  node['host']))
@@ -410,14 +410,15 @@ class DUTSetup(object):
 
         for i in range(3):
             logger.trace('Try number {0}: Get PCI device driver'.format(i))
+
             cmd = 'lspci -vmmks {0}'.format(pci_addr)
             ret_code, stdout, _ = ssh.exec_command(cmd)
-            if int(ret_code) != 0:
+            if int(ret_code):
                 raise RuntimeError("'{0}' failed on '{1}'"
                                    .format(cmd, node['host']))
 
             for line in stdout.splitlines():
-                if len(line) == 0:
+                if not line:
                     continue
                 name = None
                 value = None
@@ -459,7 +460,7 @@ class DUTSetup(object):
         cmd = 'grep -w {0} /proc/modules'.format(module)
         ret_code, _, _ = ssh.exec_command(cmd)
 
-        if int(ret_code) != 0:
+        if int(ret_code):
             if force_load:
                 # Module is not loaded and we want to load it
                 DUTSetup.kernel_module_load(node, module)
@@ -513,7 +514,7 @@ class DUTSetup(object):
 
         ret_code, _, _ = ssh.exec_command_sudo("modprobe {0}".format(module))
 
-        if int(ret_code) != 0:
+        if int(ret_code):
             raise RuntimeError('Failed to load {0} kernel module on host {1}'.
                                format(module, node['host']))
 
@@ -567,13 +568,13 @@ class DUTSetup(object):
 
                 cmd = "[[ -f /etc/redhat-release ]]"
                 return_code, _, _ = ssh.exec_command(cmd)
-                if int(return_code) == 0:
+                if not int(return_code):
                     # workaroud - uninstall existing vpp installation until
                     # start-testcase script is updated on all virl servers
                     rpm_pkgs_remove = "vpp*"
                     cmd_u = 'yum -y remove "{0}"'.format(rpm_pkgs_remove)
                     r_rcode, _, r_err = ssh.exec_command_sudo(cmd_u, timeout=90)
-                    if int(r_rcode) != 0:
+                    if int(r_rcode):
                         raise RuntimeError('Failed to remove previous VPP'
                                            'installation on host {0}:\n{1}'
                                            .format(node['host'], r_err))
@@ -582,7 +583,7 @@ class DUTSetup(object):
                                              for pkg in vpp_rpm_pkgs) + "*.rpm"
                     cmd_i = "rpm -ivh {0}".format(rpm_pkgs)
                     ret_code, _, err = ssh.exec_command_sudo(cmd_i, timeout=90)
-                    if int(ret_code) != 0:
+                    if int(ret_code):
                         raise RuntimeError('Failed to install VPP on host {0}:'
                                            '\n{1}'.format(node['host'], err))
                     else:
@@ -595,7 +596,7 @@ class DUTSetup(object):
                     deb_pkgs_remove = "vpp*"
                     cmd_u = 'apt-get purge -y "{0}"'.format(deb_pkgs_remove)
                     r_rcode, _, r_err = ssh.exec_command_sudo(cmd_u, timeout=90)
-                    if int(r_rcode) != 0:
+                    if int(r_rcode):
                         raise RuntimeError('Failed to remove previous VPP'
                                            'installation on host {0}:\n{1}'
                                            .format(node['host'], r_err))
@@ -603,7 +604,7 @@ class DUTSetup(object):
                                              for pkg in vpp_deb_pkgs) + "*.deb"
                     cmd_i = "dpkg -i --force-all {0}".format(deb_pkgs)
                     ret_code, _, err = ssh.exec_command_sudo(cmd_i, timeout=90)
-                    if int(ret_code) != 0:
+                    if int(ret_code):
                         raise RuntimeError('Failed to install VPP on host {0}:'
                                            '\n{1}'.format(node['host'], err))
                     else:
diff --git a/resources/libraries/python/DropRateSearch.py b/resources/libraries/python/DropRateSearch.py
index 912d2e9f53..9b7c46668d 100644
--- a/resources/libraries/python/DropRateSearch.py
+++ b/resources/libraries/python/DropRateSearch.py
@@ -403,10 +403,9 @@ class DropRateSearch(object):
         while True:
             res = []
             for dummy in range(self._max_attempts):
-                res.append(self.measure_loss(rate, self._frame_size,
-                                             self._loss_acceptance,
-                                             self._loss_acceptance_type,
-                                             traffic_type))
+                res.append(self.measure_loss(
+                    rate, self._frame_size, self._loss_acceptance,
+                    self._loss_acceptance_type, traffic_type))
 
             res = self._get_res_based_on_search_type(res)
 
@@ -475,11 +474,10 @@ class DropRateSearch(object):
         :rtype: tuple
         :raises Exception: If search failed.
         """
-        if self._search_result == SearchResults.FAILURE:
-            raise Exception('Search FAILED')
-        elif self._search_result in [SearchResults.SUCCESS,
-                                     SearchResults.SUSPICIOUS]:
+        if self._search_result in [
+                SearchResults.SUCCESS, SearchResults.SUSPICIOUS]:
             return self._search_result_rate, self.get_latency()
+        raise Exception('Search FAILED')
 
     def binary_search(self, b_min, b_max, traffic_type, skip_max_rate=False,
                       skip_warmup=False):
diff --git a/resources/libraries/python/IPv4NodeAddress.py b/resources/libraries/python/IPv4NodeAddress.py
index 27d55b7bb6..de96c189e5 100644
--- a/resources/libraries/python/IPv4NodeAddress.py
+++ b/resources/libraries/python/IPv4NodeAddress.py
@@ -26,26 +26,33 @@ IPV4_NETWORKS = ['192.168.{}.0/24'.format(i) for i in range(1, 100)]
 
 
 class IPv4NetworkGenerator(object):
-    """IPv4 network generator."""
+    """IPv4 network generator.
+
+    TODO: Conform to https://docs.python.org/2/library/stdtypes.html#typeiter
+    """
+
     def __init__(self, networks):
-        """
+        """Populate internal list of valid networks.
+
         :param networks: List of strings containing IPv4 subnet
-        with prefix length.
+            with prefix length.
         :type networks: list
+        :raise RuntimeError: If no IPv4 networks are added.
         """
-        self._networks = list()
+        self._networks = []
         for network in networks:
             net = IPv4Network(unicode(network))
             self._networks.append(net)
-        if len(self._networks) == 0:
-            raise Exception('No IPv4 networks')
+        if not self._networks:
+            raise RuntimeError("No IPv4 networks")
 
     def next_network(self):
-        """
+        """Pop and return network from internal list.
+
         :returns: Next network in form (IPv4Network, subnet).
         :raises StopIteration: If there are no more elements.
         """
-        if len(self._networks):
+        if self._networks:
             return self._networks.pop()
         else:
             raise StopIteration()
diff --git a/resources/libraries/python/IPv4Setup.py b/resources/libraries/python/IPv4Setup.py
index f9b067d0d8..b018bceacf 100644
--- a/resources/libraries/python/IPv4Setup.py
+++ b/resources/libraries/python/IPv4Setup.py
@@ -118,8 +118,8 @@ class IPv4Node(object):
 
 class Tg(IPv4Node):
     """Traffic generator node"""
-    def __init__(self, node_info):
-        super(Tg, self).__init__(node_info)
+
+    # Implicit constructor is inherited.
 
     def _execute(self, cmd):
         """Executes the specified command on TG using SSH.
@@ -179,8 +179,8 @@ class Tg(IPv4Node):
 
 class Dut(IPv4Node):
     """Device under test"""
-    def __init__(self, node_info):
-        super(Dut, self).__init__(node_info)
+
+    # Implicit contructor is inherited.
 
     def get_sw_if_index(self, interface):
         """Get sw_if_index of specified interface from current node.
diff --git a/resources/libraries/python/IPv6Setup.py b/resources/libraries/python/IPv6Setup.py
index e0de406a4a..260c08b198 100644
--- a/resources/libraries/python/IPv6Setup.py
+++ b/resources/libraries/python/IPv6Setup.py
@@ -13,8 +13,8 @@
 
 """Library to set up IPv6 in topology."""
 
-from robot.api import logger
 from ipaddress import IPv6Network
+from robot.api import logger
 
 from resources.libraries.python.ssh import SSH
 from resources.libraries.python.topology import NodeType, Topology
@@ -25,17 +25,22 @@ from resources.libraries.python.VatExecutor import VatTerminal, VatExecutor
 class IPv6Networks(object):
     """IPv6 network iterator.
 
-    :param networks: List of the available IPv6 networks.
-    :type networks: list
+    TODO: Conform to https://docs.python.org/2/library/stdtypes.html#typeiter
     """
+
     def __init__(self, networks):
-        self._networks = list()
+        """Initialize internal list of valid networks.
+
+        :param networks: List of the available IPv6 networks.
+        :type networks: list
+        :raise RuntimeError: If no networks were added.
+        """
+        self._networks = []
         for network in networks:
             net = IPv6Network(unicode(network))
             self._networks.append(net)
-        num = len(self._networks)
-        if num == 0:
-            raise Exception('No IPv6 networks')
+        if not self._networks:
+            raise RuntimeError('No IPv6 networks')
 
     def next_network(self):
         """Get the next element of the iterator.
@@ -44,7 +49,7 @@ class IPv6Networks(object):
         :rtype: IPv6Network object
         :raises StopIteration: If there is no more elements.
         """
-        if len(self._networks):
+        if self._networks:
             return self._networks.pop()
         else:
             raise StopIteration()
diff --git a/resources/libraries/python/InterfaceUtil.py b/resources/libraries/python/InterfaceUtil.py
index 94cee5ecbc..e43935eb7b 100644
--- a/resources/libraries/python/InterfaceUtil.py
+++ b/resources/libraries/python/InterfaceUtil.py
@@ -783,11 +783,10 @@ class InterfaceUtil(object):
                 "tap_dump.vat")
         if name is None:
             return response[0]
-        else:
-            for item in response[0]:
-                if name == item['dev_name']:
-                    return item
-            return {}
+        for item in response[0]:
+            if name == item['dev_name']:
+                return item
+        return {}
 
     @staticmethod
     def create_subinterface(node, interface, sub_id, outer_vlan_id=None,
diff --git a/resources/libraries/python/MacSwap.py b/resources/libraries/python/MacSwap.py
index 1ec6a5d216..ebcf95eae2 100644
--- a/resources/libraries/python/MacSwap.py
+++ b/resources/libraries/python/MacSwap.py
@@ -59,5 +59,3 @@ class MacSwap(object):
         else:
             raise ValueError('Node {} has not DUT NodeType: "{}"'.
                              format(node['host'], node['type']))
-
-
diff --git a/resources/libraries/python/Memif.py b/resources/libraries/python/Memif.py
index acde3ecc17..76e775fcca 100644
--- a/resources/libraries/python/Memif.py
+++ b/resources/libraries/python/Memif.py
@@ -145,7 +145,7 @@ class Memif(object):
             memif_data = memif_data.replace(garbage, '')
 
         for line in memif_data.splitlines():
-            if line.startswith('Sending') or len(line) == 0:
+            if not line or line.startswith('Sending'):
                 continue
             elif line.startswith('memif'):
                 if memif_name:
@@ -177,7 +177,7 @@ class Memif(object):
         :param sw_if_idx: DUT node.
         :type node: dict
         :type sw_if_idx: int
-        :returns: Memif interface name.
+        :returns: Memif interface name, or None if not found.
         :rtype: str
         """
         with VatTerminal(node, json_param=False) as vat:
@@ -196,7 +196,7 @@ class Memif(object):
         :param sw_if_idx: DUT node.
         :type node: dict
         :type sw_if_idx: int
-        :returns: Memif interface MAC address.
+        :returns: Memif interface MAC address, or None if not found.
         :rtype: str
         """
         with VatTerminal(node, json_param=False) as vat:
@@ -205,6 +205,7 @@ class Memif(object):
             for item in memif_data:
                 if memif_data[item]['sw_if_index'] == str(sw_if_idx):
                     return memif_data[item].get('mac', None)
+        return None
 
     @staticmethod
     def vpp_get_memif_interface_socket(node, sw_if_idx):
@@ -214,7 +215,7 @@ class Memif(object):
         :param sw_if_idx: DUT node.
         :type node: dict
         :type sw_if_idx: int
-        :returns: Memif interface socket path.
+        :returns: Memif interface socket path, or None if not found.
         :rtype: str
         """
         with VatTerminal(node, json_param=False) as vat:
@@ -223,6 +224,7 @@ class Memif(object):
             for item in memif_data:
                 if memif_data[item]['sw_if_index'] == str(sw_if_idx):
                     return memif_data[item].get('socket', None)
+        return None
 
     @staticmethod
     def vpp_get_memif_interface_id(node, sw_if_idx):
@@ -232,7 +234,7 @@ class Memif(object):
         :param sw_if_idx: DUT node.
         :type node: dict
         :type sw_if_idx: int
-        :returns: Memif interface ID.
+        :returns: Memif interface ID, or None if not found.
         :rtype: int
         """
         with VatTerminal(node, json_param=False) as vat:
@@ -241,6 +243,7 @@ class Memif(object):
             for item in memif_data:
                 if memif_data[item]['sw_if_index'] == str(sw_if_idx):
                     return int(memif_data[item].get('id', None))
+        return None
 
     @staticmethod
     def vpp_get_memif_interface_role(node, sw_if_idx):
@@ -250,7 +253,7 @@ class Memif(object):
         :param sw_if_idx: DUT node.
         :type node: dict
         :type sw_if_idx: int
-        :returns: Memif interface role.
+        :returns: Memif interface role, or None if not found.
         :rtype: int
         """
         with VatTerminal(node, json_param=False) as vat:
@@ -259,3 +262,4 @@ class Memif(object):
             for item in memif_data:
                 if memif_data[item]['sw_if_index'] == str(sw_if_idx):
                     return memif_data[item].get('role', None)
+        return None
diff --git a/resources/libraries/python/NATUtil.py b/resources/libraries/python/NATUtil.py
index ab97e05dcc..e08a6daf82 100644
--- a/resources/libraries/python/NATUtil.py
+++ b/resources/libraries/python/NATUtil.py
@@ -197,9 +197,9 @@ class NATUtil(object):
             items = line.split(" ")
             while "" in items:
                 items.remove("")
-            if len(items) == 0:
+            if not items:
                 continue
-            elif len(items) == 4:
+            if len(items) == 4:
                 # no ports were returned
                 data.append({
                     "local_address": items[0],
@@ -246,9 +246,9 @@ class NATUtil(object):
             for trash in ("", "vat#"):
                 while trash in items:
                     items.remove(trash)
-            if len(items) == 0:
+            if not items:
                 continue
-            elif len(items) == 3:
+            if len(items) == 3:
                 data.append({
                     # items[0] is the table header - "sw_if_index"
                     "sw_if_index": items[1],
diff --git a/resources/libraries/python/NodePath.py b/resources/libraries/python/NodePath.py
index f41103046f..ec84a8b08b 100644
--- a/resources/libraries/python/NodePath.py
+++ b/resources/libraries/python/NodePath.py
@@ -151,8 +151,7 @@ class NodePath(object):
         """
         if not self._path_iter:
             return None, None
-        else:
-            return self._path_iter.pop()
+        return self._path_iter.pop()
 
     def first_interface(self):
         """Return first interface on the path.
diff --git a/resources/libraries/python/SchedUtils.py b/resources/libraries/python/SchedUtils.py
index ec18b98dac..b4c57217bd 100644
--- a/resources/libraries/python/SchedUtils.py
+++ b/resources/libraries/python/SchedUtils.py
@@ -45,7 +45,7 @@ class SchedUtils(object):
                     print 'Reading VPP worker thread PID failed.'
                 else:
                     for pid in out.split("\n"):
-                        if len(pid) > 0 and pid[0] != "#":
+                        if pid and pid[0] != '#':
                             SchedUtils.set_proc_scheduling_rr(node, int(pid))
                     break
         else:
diff --git a/resources/libraries/python/Tap.py b/resources/libraries/python/Tap.py
index ffcd00cdaf..6b8ae87c04 100644
--- a/resources/libraries/python/Tap.py
+++ b/resources/libraries/python/Tap.py
@@ -120,7 +120,7 @@ class Tap(object):
         :raises RuntimeError: Specified interface was not found.
         """
         tap_if = InterfaceUtil.tap_dump(node, tap_name)
-        if len(tap_if) == 0:
+        if not tap_if:
             raise RuntimeError(
                 'Tap interface :{} does not exist'.format(tap_name))
 
diff --git a/resources/libraries/python/VatHistory.py b/resources/libraries/python/VatHistory.py
index e273746f9b..ffc1644f1b 100644
--- a/resources/libraries/python/VatHistory.py
+++ b/resources/libraries/python/VatHistory.py
@@ -71,12 +71,12 @@ class VatHistory(object):
         :type node: dict
         """
         if node['type'] == NodeType.DUT:
-            sequence = "\nno VAT command executed"\
-                if len(DICT__DUTS_VAT_HISTORY[node['host']]) == 0\
-                else "".join("\n{}".format(cmd)
-                             for cmd in DICT__DUTS_VAT_HISTORY[node['host']])
-            logger.trace("{0} VAT command history:{1}\n".
-                         format(node['host'], sequence))
+            sequence = "\nno VAT command executed"
+            if DICT__DUTS_VAT_HISTORY[node['host']]:
+                sequence = "".join(["\n{}".format(
+                    cmd) for cmd in DICT__DUTS_VAT_HISTORY[node['host']]])
+            logger.trace(
+                "{0} VAT command history:{1}\n".format(node['host'], sequence))
 
     @staticmethod
     def show_vat_history_on_all_duts(nodes):
diff --git a/resources/libraries/python/VppCounters.py b/resources/libraries/python/VppCounters.py
index 5dc14a9a4e..b2c3b01c60 100644
--- a/resources/libraries/python/VppCounters.py
+++ b/resources/libraries/python/VppCounters.py
@@ -208,8 +208,7 @@ class VppCounters(object):
             vat.vat_terminal_exec_cmd('want_stats enable')
             for _ in range(0, 12):
                 stats_table = vat.vat_terminal_exec_cmd('dump_stats_table')
-                if_counters = stats_table['interface_counters']
-                if len(if_counters) > 0:
+                if stats_table['interface_counters']:
                     self._stats_table = stats_table
                     return stats_table
                 time.sleep(1)
@@ -259,15 +258,15 @@ class VppCounters(object):
             return 0
 
         if_counters = self._stats_table.get('interface_counters')
-        if if_counters is None or len(if_counters) == 0:
+        if not if_counters:
             logger.trace('No interface counters.')
             return 0
         for counter in if_counters:
             if counter['vnet_counter_type'] == version:
                 data = counter['data']
                 return data[if_index]
-        logger.trace('{i} {v} counter not found.'.format(i=interface,
-                                                         v=version))
+        logger.trace('{i} {v} counter not found.'.format(
+            i=interface, v=version))
         return 0
 
     @staticmethod
diff --git a/resources/libraries/python/ssh.py b/resources/libraries/python/ssh.py
index 7368c6980a..06cd96010d 100644
--- a/resources/libraries/python/ssh.py
+++ b/resources/libraries/python/ssh.py
@@ -370,7 +370,7 @@ def exec_cmd(node, cmd, timeout=600, sudo=False):
         raise TypeError('Node parameter is None')
     if cmd is None:
         raise TypeError('Command parameter is None')
-    if len(cmd) == 0:
+    if not cmd:
         raise ValueError('Empty command parameter')
 
     ssh = SSH()
diff --git a/resources/libraries/python/topology.py b/resources/libraries/python/topology.py
index d60bed1b5b..82516beb6b 100644
--- a/resources/libraries/python/topology.py
+++ b/resources/libraries/python/topology.py
@@ -394,13 +394,13 @@ class Topology(object):
         :type node: dict
         :type iface_key: str/int
         :returns: Return sw_if_index or None if not found.
+        :rtype: int or None
         """
         try:
             if isinstance(iface_key, basestring):
                 return node['interfaces'][iface_key].get('vpp_sw_index')
             # TODO: use only iface_key, do not use integer
-            else:
-                return int(iface_key)
+            return int(iface_key)
         except (KeyError, ValueError):
             return None
 
@@ -416,11 +416,10 @@ class Topology(object):
         :raises TypeError: If provided interface name is not a string.
         """
         try:
-            if isinstance(iface_name, basestring):
-                iface_key = Topology.get_interface_by_name(node, iface_name)
-                return node['interfaces'][iface_key].get('vpp_sw_index')
-            else:
+            if not isinstance(iface_name, basestring):
                 raise TypeError("Interface name must be a string.")
+            iface_key = Topology.get_interface_by_name(node, iface_name)
+            return node['interfaces'][iface_key].get('vpp_sw_index')
         except (KeyError, ValueError):
             return None
 
@@ -565,6 +564,8 @@ class Topology(object):
         :param iface_keys: Interface keys for lookup.
         :type node: dict
         :type iface_keys: strings
+        :returns: Numa node of most given interfaces or 0.
+        :rtype: int
         """
         numa_list = []
         for if_key in iface_keys:
@@ -575,12 +576,11 @@ class Topology(object):
 
         numa_cnt_mc = Counter(numa_list).most_common()
 
-        if len(numa_cnt_mc) > 0 and numa_cnt_mc[0][0] != -1:
+        if numa_cnt_mc and numa_cnt_mc[0][0] != -1:
             return numa_cnt_mc[0][0]
-        elif len(numa_cnt_mc) > 1 and numa_cnt_mc[0][0] == -1:
+        if len(numa_cnt_mc) > 1 and numa_cnt_mc[0][0] == -1:
             return numa_cnt_mc[1][0]
-        else:
-            return 0
+        return 0
 
     @staticmethod
     def get_interface_mac(node, iface_key):
@@ -650,6 +650,7 @@ class Topology(object):
                     continue
                 if if_val['link'] == link_name:
                     return node_data, if_key
+        return None
 
     @staticmethod
     def get_interface_pci_addr(node, iface_key):
@@ -716,8 +717,8 @@ class Topology(object):
         :param filter_list: Link filter criteria.
         :type node: dict
         :type filter_list: list of strings
-        :returns: List of strings representing link names occupied by the node.
-        :rtype: list
+        :returns: List of link names occupied by the node.
+        :rtype: None or list of string
         """
         interfaces = node['interfaces']
         link_names = []
@@ -732,7 +733,7 @@ class Topology(object):
                                  .format(str(interface)))
                 else:
                     link_names.append(interface['link'])
-        if len(link_names) == 0:
+        if not link_names:
             link_names = None
         return link_names
 
@@ -782,15 +783,14 @@ class Topology(object):
         :param node2: Connected node.
         :type node1: dict
         :type node2: dict
-        :returns: Name of link connecting the two nodes together.
+        :returns: Name of a link connecting the two nodes together.
         :rtype: str
         :raises RuntimeError: If no links are found.
         """
         connecting_links = self.get_active_connecting_links(node1, node2)
-        if len(connecting_links) == 0:
+        if not connecting_links:
             raise RuntimeError("No links connecting the nodes were found")
-        else:
-            return connecting_links[0]
+        return connecting_links[0]
 
     @keyword('Get egress interfaces name on "${node1}" for link with '
              '"${node2}"')
@@ -806,7 +806,7 @@ class Topology(object):
         """
         interfaces = []
         links = self.get_active_connecting_links(node1, node2)
-        if len(links) == 0:
+        if not links:
             raise RuntimeError('No link between nodes')
         for interface in node1['interfaces'].values():
             link = interface.get('link')