fix some details in graphs (found by lgtm)

Author: fchapoton

src/sage/graphs/graph_input.py

@@ -371,6 +371,8 @@ def from_oriented_incidence_matrix(G, M, loops=False, multiedges=False, weighted
     - ``loops``, ``multiedges``, ``weighted`` -- booleans (default: ``False``);
       whether to consider the graph as having loops, multiple edges, or weights
 
+    .. NOTE:: ``weighted`` is currently ignored.
+
     EXAMPLES::
 
         sage: from sage.graphs.graph_input import from_oriented_incidence_matrix
@@ -426,8 +428,6 @@ def from_oriented_incidence_matrix(G, M, loops=False, multiedges=False, weighted
             positions.append(tuple(NZ))
         else:
             positions.append((NZ[1], NZ[0]))
-    if weighted is None:
-        weighted = False
     if multiedges is None:
         total = len(positions)
         multiedges = len(set(positions)) < total

src/sage/graphs/partial_cube.py

@@ -166,7 +166,6 @@ def depth_first_traversal(G, start):
         sage: t = list(sage.graphs.partial_cube.depth_first_traversal(H, '00'))
         sage: len(t)
         16
-
     """
     neighbors = G.neighbor_out_iterator
     seen = set()
@@ -286,7 +285,7 @@ def is_partial_cube(G, certificate=False):
     # Initial sanity check: are there few enough edges?
     # Needed so that we don't try to use union-find on a dense
     # graph and incur superquadratic runtimes.
-    if 1 << (2*G.size()//n) > n:
+    if 1 << (2 * G.size() // n) > n:
         return fail
 
     # Check for bipartiteness.
@@ -399,13 +398,13 @@ def is_partial_cube(G, certificate=False):
 
     # Rest of data structure: point from states to list and list to states
     state_to_active_token = {v: -1 for v in g}
-    token_to_states = [[] for i in activeTokens]  # (i.e. vertices on which each token acts)
+    token_to_states = [[] for _ in activeTokens]  # (i.e. vertices on which each token acts)
 
     def scan(v):
         """
         Find the next token that is effective for v.
         """
-        a = next(i for i in range(state_to_active_token[v]+1, len(activeTokens))
+        a = next(i for i in range(state_to_active_token[v] + 1, len(activeTokens))
                  if activeTokens[i] is not None and activeTokens[i] in action[v])
         state_to_active_token[v] = a
         token_to_states[a].append(v)

src/sage/graphs/schnyder.py

@@ -213,7 +213,6 @@ def _normal_label(g, comb_emb, external_face):
         except Exception:
             raise RuntimeError('Contractible list is empty but graph still has %d vertices.  (Expected 3.)' % g.order())
 
-            break
         # going to contract v
         v_neighbors = Set(g.neighbors(v))
         contracted.append((v, v_neighbors,