diff --git a/grandalf/graphs.py b/grandalf/graphs.py
index b008b78..24e2b01 100644
--- a/grandalf/graphs.py
+++ b/grandalf/graphs.py
@@ -15,7 +15,6 @@
 # published under GPLv2 license or EPLv1 license
 
 from .utils import Poset
-from operator import attrgetter
 
 #------------------------------------------------------------------------------
 
@@ -133,6 +132,9 @@ def index(self):
     def __lt__(self,v):
         return 0
 
+    def __gt__(self,v):
+        return 0
+
     def __getstate__(self):
         return (self.index,self.data)
 
@@ -165,7 +167,7 @@ def __init__(self,x,y,w=1,data=None,connect=False):
         self.w = w
         self.data = data
         self.feedback = False
-        if connect and (x.c==None or y.c==None):
+        if connect and (x.c is None or y.c is None):
             c = x.c or y.c
             c.add_edge(self)
 
@@ -187,6 +189,9 @@ def detach(self):
     def __lt__(self,v):
         return 0
 
+    def __gt__(self,v):
+        return 0
+
     def __getstate__(self):
         xi,yi = (self.v[0].index,self.v[1].index)
         return (xi,yi,self.w,self.data,self.feedback)
diff --git a/grandalf/layouts.py b/grandalf/layouts.py
index 4f70d82..e2461c8 100644
--- a/grandalf/layouts.py
+++ b/grandalf/layouts.py
@@ -20,7 +20,6 @@
 import importlib
 from bisect import bisect
 from sys import getrecursionlimit,setrecursionlimit
-from operator import attrgetter
 
 from grandalf.utils import *
 
@@ -154,6 +153,9 @@ class Layer(list):
     __x    = 1.
     ccount = None
 
+    def __eq__(self,other):
+        return super().__eq__(other)
+
     def __str__(self):
         s  = '<Layer %d'%self.__r
         s += ', len=%d'%len(self)
@@ -383,10 +385,10 @@ def init_all(self,roots=None,inverted_edges=None,optimize=False):
         if self.initdone: return
         # For layered sugiyama algorithm, the input graph must be acyclic,
         # so we must provide a list of root nodes and a list of inverted edges.
-        if roots==None:
+        if roots is None:
             roots = [v for v in self.g.sV if len(v.e_in())==0]
-        if inverted_edges==None:
-            L = self.g.get_scs_with_feedback(roots)
+        if inverted_edges is None:
+            _ = self.g.get_scs_with_feedback(roots)
             inverted_edges = [x for x in self.g.sE if x.feedback]
         self.alt_e = inverted_edges
         # assign rank to all vertices:
@@ -664,7 +666,7 @@ def _coord_vertical_alignment(self):
                         else:       vpair = (um,vk)
                         # if vk<->um link is used for alignment
                         if (vpair not in self.conflicts) and \
-                           (r==None or dirh*r<dirh*m):
+                           ((r is None) or (dirh*r<dirh*m)):
                             g[um].align = vk
                             g[vk].root = g[um].root
                             g[vk].align = g[vk].root
@@ -713,7 +715,7 @@ def _coord_horizontal_compact(self):
     # TODO: rewrite in iterative form to avoid recursion limit...
     def __place_block(self,v):
         g = self.grx
-        if g[v].X==None:
+        if g[v].X is None:
             # every block is initially placed at x=0
             g[v].X = 0.0
             # place block in which v belongs:
@@ -749,7 +751,6 @@ def draw_edges(self):
         for e in self.g.E():
             if hasattr(e,'view'):
                 l=[]
-                r0,r1 = None,None
                 if e in self.ctrls:
                     D = self.ctrls[e]
                     r0,r1 = self.grx[e.v[0]].rank,self.grx[e.v[1]].rank
diff --git a/grandalf/routing.py b/grandalf/routing.py
index c38bdb6..cdafffd 100644
--- a/grandalf/routing.py
+++ b/grandalf/routing.py
@@ -96,8 +96,8 @@ def _round_corners(pts, round_at_distance):
                         continue
                 generated = _gen_smoother_middle_points_from_3_points(
                     [p1, p2, p3], calc_with_distance)
-                for i in generated:
-                    new_lst.append(i)
+                for j in generated:
+                    new_lst.append(j)
             new_lst.append(pts[-1])
             pts = new_lst
             calc_with_distance /= 2.
diff --git a/grandalf/utils/dot.py b/grandalf/utils/dot.py
index e3fcefc..a110bb5 100644
--- a/grandalf/utils/dot.py
+++ b/grandalf/utils/dot.py
@@ -331,7 +331,7 @@ def p_E(self,p):
             try:
                 L = p[1]
                 L.append(Dot.edge(L[-1].n2,p[2]))
-            except:
+            except Exception:
                 L = []
                 L.append(Dot.edge(p[1],p[2]))
             p[0] = L
@@ -389,7 +389,7 @@ def parse(self,data):
         except AttributeError:
             self.lexer.build(reflags=lex.re.UNICODE)
             self.parser.build()
-        except:
+        except Exception:
             print('unexpected error')
             return None
         try:
diff --git a/grandalf/utils/geometry.py b/grandalf/utils/geometry.py
index 1493fee..afecb80 100644
--- a/grandalf/utils/geometry.py
+++ b/grandalf/utils/geometry.py
@@ -7,7 +7,7 @@
 from .poset import *
 from .dot import *
 
-from math import atan,atan2,degrees,sqrt
+from math import atan2,sqrt
 from random import SystemRandom
 
 #------------------------------------------------------------------------------
diff --git a/grandalf/utils/linalg.py b/grandalf/utils/linalg.py
index e1e8fc4..4719364 100644
--- a/grandalf/utils/linalg.py
+++ b/grandalf/utils/linalg.py
@@ -20,7 +20,7 @@ def _mkslice(i,n):
 
 def make_ij_slices(f):
     def wrapper(self,ij,*args):
-        I = slice(0,self.n,1)
+        #I = slice(0,self.n,1)
         J = slice(0,self.p,1)
         if isinstance(ij,tuple):
             I = _mkslice(ij[0],self.n)
diff --git a/grandalf/utils/nx.py b/grandalf/utils/nx.py
index 2320309..bc0e62b 100644
--- a/grandalf/utils/nx.py
+++ b/grandalf/utils/nx.py
@@ -3,6 +3,10 @@
 # published under GPLv2 license or EPLv1 license
 # Contributor(s): Fabio Zadrozny
 
+__all__=['convert_grandalf_graph_to_networkx_graph',
+         'convert_nextworkx_graph_to_grandalf',
+        ]
+
 #Some utilities to interact with networkx.
 
 #Converts a grandalf graph to a networkx graph.
diff --git a/grandalf/utils/poset.py b/grandalf/utils/poset.py
index aeda219..911105b 100644
--- a/grandalf/utils/poset.py
+++ b/grandalf/utils/poset.py
@@ -5,6 +5,8 @@
 
 from collections import OrderedDict
 
+__all__ = ['Poset']
+
 #------------------------------------------------------------------------------
 # Poset class implements a set but allows to interate over the elements in a
 # deterministic way and to get specific objects in the set.
diff --git a/setup.py b/setup.py
index b1cc4cf..89fff62 100755
--- a/setup.py
+++ b/setup.py
@@ -1,6 +1,4 @@
-from setuptools import setup, find_packages
-from codecs import open
-from os import path
+from setuptools import setup
 
 long_descr = '''
 Grandalf is a python package made for experimentations with graphs and drawing
diff --git a/tests/test_layouts.py b/tests/test_layouts.py
index 86d7616..148a277 100644
--- a/tests/test_layouts.py
+++ b/tests/test_layouts.py
@@ -81,7 +81,8 @@ def create_scenario():
 
 class CustomRankingSugiyamaLayout(SugiyamaLayout):
 
-    def init_all(self, roots=None, inverted_edges=None, initial_ranking=None):
+    def init_all(self, roots=None, inverted_edges=None, optimize=False,
+                 initial_ranking=None):
         '''
         :param dict{vertex:int} initial_ranking:
             The initial ranking of each vertex if passed
@@ -92,13 +93,13 @@ def init_all(self, roots=None, inverted_edges=None, initial_ranking=None):
             nblayers = max(initial_ranking.keys())+1
             self.layers = [Layer([]) for l in range(nblayers)]
 
-        SugiyamaLayout.init_all(self, roots=roots, inverted_edges=inverted_edges)
+        super().init_all(roots, inverted_edges, False)
 
     def _rank_init(self,unranked):
         assert self.dag
 
         if not hasattr(self, 'initial_ranking'):
-            SugiyamaLayout._rank_init(self, unranked)
+            super()._rank_init(unranked)
         else:
             for rank, vertices in sorted(self.initial_ranking.items()):
                 for v in vertices:
@@ -120,7 +121,7 @@ def test_sugiyama_ranking():
     gr, data_to_vertex = create_scenario()
     sug = SugiyamaLayout(gr)
     sug.route_edge = route_with_rounded_corners
-    sug.init_all()
+    sug.init_all(None,None,False)
     # rank 0: v4      v0
     #          \     / |
     # rank 1:   \   v1 |
@@ -151,7 +152,7 @@ def test_sugiyama_custom_ranking():
         3: [data_to_vertex['v2']],
         4: [data_to_vertex['v3']],
     }
-    sug.init_all(initial_ranking=rank_to_data)
+    sug.init_all(None,None,False,initial_ranking=rank_to_data)
     # rank 0: v4      v0
     #          \     / |
     # rank 1:   \   v1 |
@@ -182,6 +183,6 @@ def test_sugiyama_custom_ranking2():
         3: [data_to_vertex['v3']],
     }
     try:
-        sug.init_all(initial_ranking=rank_to_data)
+        sug.init_all(None,None,False,initial_ranking=rank_to_data)
     except ValueError as e:
         assert e.message == 'bad ranking'