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>

1 files changed, 15 insertions, 8 deletions

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()