gh-40032: various small fixes, some after ruff
    
various small changes, mostly cosmetic

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #40032
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager

src/sage/algebras/fusion_rings/fusion_double.py

@@ -257,8 +257,8 @@ def s_ij(self, i, j, unitary=False, base_coercion=True):
         """
         sum_val = ZZ.zero()
         G = self._G
-        [i] = list(i._monomial_coefficients)
-        [j] = list(j._monomial_coefficients)
+        i, = list(i._monomial_coefficients)
+        j, = list(j._monomial_coefficients)
         a = self._elt[i]
         b = self._elt[j]
         for g in G:

src/sage/combinat/crystals/fast_crystals.py

@@ -220,9 +220,9 @@ def _type_bc_init(self, l1, l2):
             4
         """
         if self._cartan_type[0] == 'B':
-            [m1, m2] = [l1+l2, l1-l2]
+            m1, m2 = l1 + l2, l1 - l2
         else:
-            [m1, m2] = [l1, l2]
+            m1, m2 = l1, l2
         for b in range(m2,-1,-1):
             for a in range(m1,m2-1,-1):
                 for c in range(b,a+1):
@@ -336,11 +336,11 @@ def weight(self):
             delpat = self.parent().delpat[self.value]
             if self.parent()._cartan_type[0] == 'A':
                 delpat = delpat + [0,]
-            [alpha1, alpha2] = self.parent().weight_lattice_realization().simple_roots()
+            alpha1, alpha2 = self.parent().weight_lattice_realization().simple_roots()
             hwv = sum(self.parent().shape[i]*self.parent().weight_lattice_realization().monomial(i) for i in range(2))
             return hwv - (delpat[0]+delpat[2])*alpha1 - (delpat[1]+delpat[3])*alpha2
 
-        def _repr_(self):
+        def _repr_(self) -> str:
             """
             EXAMPLES::
 

src/sage/combinat/parallelogram_polyomino.py

@@ -695,7 +695,7 @@ def rotate(pos, angle):
 
             The rotated position.
             """
-            [x, y] = pos
+            x, y = pos
             return [x*cos(angle) - y*sin(angle), x*sin(angle) + y*cos(angle)]
 
         def mirror(pos, axe):
@@ -770,8 +770,8 @@ def draw_line(self, v1, v2, color=None, size=None):
             color = self._color_line
         if size is None:
             size = self._line_size
-        [x1, y1] = self.XY(v1)
-        [x2, y2] = self.XY(v2)
+        x1, y1 = self.XY(v1)
+        x2, y2 = self.XY(v2)
         return "\n  \\draw[color=%s, line width=%s] (%f, %f) -- (%f, %f);" % (
             color, size, float(x1), float(y1), float(x2), float(y2)
         )
@@ -844,14 +844,14 @@ def draw_point(self, p1, color=None, size=None):
             color = self._color_point
         if size is None:
             size = self._point_size
-        [x1, y1] = self.XY(p1)
+        x1, y1 = self.XY(p1)
         return "\n  \\filldraw[color=%s] (%f, %f) circle (%spt);" % (
             color, float(x1), float(y1), size
         )
 
 
 class ParallelogramPolyomino(ClonableList,
-        metaclass=InheritComparisonClasscallMetaclass):
+                             metaclass=InheritComparisonClasscallMetaclass):
     r"""
     Parallelogram Polyominoes.
 

src/sage/combinat/words/finite_word.py

@@ -1684,9 +1684,9 @@ def reduced_rauzy_graph(self, n):
             g.allow_loops(True)
             g.allow_multiple_edges(True)
             for v in l:
-                [i] = g.neighbors_in(v)
-                [o] = g.neighbors_out(v)
-                g.add_edge(i, o, g.edge_label(i, v)[0]*g.edge_label(v, o)[0])
+                i = next(g.neighbor_in_iterator(v))
+                o = next(g.neighbor_out_iterator(v))
+                g.add_edge(i, o, g.edge_label(i, v)[0] * g.edge_label(v, o)[0])
                 g.delete_vertex(v)
         return g
 

src/sage/dynamics/arithmetic_dynamics/wehlerK3.py

@@ -1140,20 +1140,20 @@ def sigmaX(self, P, **kwds):
                     raise TypeError("%s fails to convert into the map's domain %s, but a `pushforward` method is not properly implemented" % (P, self))
         pt = list(P[0]) + [0, 0, 0]
         if P[1][0] != 0:
-            [a,b,c] = [P[1][0]*self.Gpoly(1, 0)(*pt),
+            a, b, c = [P[1][0]*self.Gpoly(1, 0)(*pt),
                        -1*P[1][0]*self.Hpoly(1, 0, 1)(*pt) - P[1][1]*self.Gpoly(1, 0)(*pt),
                        -P[1][0]*self.Hpoly(1, 0, 2)(*pt) - P[1][2]*self.Gpoly(1, 0)(*pt)]
         elif P[1][1] != 0:
-            [a,b,c] = [-1*P[1][1]*self.Hpoly(1, 0, 1)(*pt)-P[1][0]*self.Gpoly(1, 1)(*pt),
+            a, b, c = [-1*P[1][1]*self.Hpoly(1, 0, 1)(*pt)-P[1][0]*self.Gpoly(1, 1)(*pt),
                         P[1][1]*self.Gpoly(1, 1)(*pt),
                        -P[1][1]*self.Hpoly(1, 1, 2)(*pt)-P[1][2]*self.Gpoly(1, 1)(*pt)]
         else:
-            [a,b,c] = [-1*P[1][2]*self.Hpoly(1, 0, 2)(*pt) - P[1][0]*self.Gpoly(1, 2)(*pt),
+            a, b, c = [-1*P[1][2]*self.Hpoly(1, 0, 2)(*pt) - P[1][0]*self.Gpoly(1, 2)(*pt),
                        -P[1][2]*self.Hpoly(1, 1, 2)(*pt) - P[1][1]*self.Gpoly(1, 2)(*pt),
                        P[1][2]*self.Gpoly(1, 2)(*pt)]
         Point = [P[0][0], P[0][1], P[0][2], a, b, c]
 
-        if [a,b,c] != [0,0,0]:
+        if any([a, b, c]):
             if normalize:
                 Point = self.point(Point,False)
                 Point.normalize_coordinates()
@@ -1237,7 +1237,7 @@ def sigmaX(self, P, **kwds):
         if len(V) == 2:
             for D in V:
                 if D[s] != 0:
-                    [a,b,c] = [D[z0], D[z1], D[z2]]
+                    a, b, c = [D[z0], D[z1], D[z2]]
         else:
             newT = [phi(tee) for tee in T]
             for i in range(2):
@@ -1278,9 +1278,9 @@ def sigmaX(self, P, **kwds):
                 raise ValueError("cannot distinguish points in the degenerate fiber")
 
             if len(V) == 1:
-                [a, b, c] = [V[0][z0], V[0][z1], V[0][z2]]
+                a, b, c = [V[0][z0], V[0][z1], V[0][z2]]
 
-            if len(V) == 0 or [a,b,c] == [0, 0, 0]:
+            if len(V) == 0 or not any([a, b, c]):
                 SS = PolynomialRing(BR, 3, 'z0, z1, z2', order='lex')
                 z0,z1,z2 = SS.gens()
                 phi = RR.hom([1, 0, z0, z1, z2], SS)
@@ -1290,7 +1290,7 @@ def sigmaX(self, P, **kwds):
                 V = phi(I).variety()
                 if len(V) > 1:
                     raise ValueError( "cannot distinguish points in the degenerate fiber")
-                [a,b,c] = [V[0][z0], V[0][z1], V[0][z2]]
+                a, b, c = [V[0][z0], V[0][z1], V[0][z2]]
 
         Point = [P[0][0], P[0][1], P[0][2], a, b, c]
         if normalize:
@@ -1384,19 +1384,19 @@ def sigmaY(self, P, **kwds):
                     raise TypeError("%s fails to convert into the map's domain %s, but a `pushforward` method is not properly implemented" % (P, self))
         pt = [0, 0, 0] + list(P[1])
         if P[0][0] != 0:
-            [a, b, c] = [P[0][0]*self.Gpoly(0, 0)(*pt),
+            a, b, c = [P[0][0]*self.Gpoly(0, 0)(*pt),
                       -1*P[0][0]*self.Hpoly(0, 0, 1)(*pt) - P[0][1]*self.Gpoly(0, 0)(*pt),
                       -P[0][0]*self.Hpoly(0, 0, 2)(*pt) - P[0][2]*self.Gpoly(0, 0)(*pt)]
         elif P[0][1] != 0:
-            [a, b, c] = [-1*P[0][1]*self.Hpoly(0, 0, 1)(*pt) - P[0][0]*self.Gpoly(0, 1)(*pt),
+            a, b, c = [-1*P[0][1]*self.Hpoly(0, 0, 1)(*pt) - P[0][0]*self.Gpoly(0, 1)(*pt),
                        P[0][1]*self.Gpoly(0, 1)(*pt),
                        -P[0][1]*self.Hpoly(0, 1, 2)(*pt) - P[0][2]*self.Gpoly(0, 1)(*pt)]
         else:
-            [a, b, c] = [-1*P[0][2]*self.Hpoly(0, 0, 2)(*pt) - P[0][0]*self.Gpoly(0, 2)(*pt),
+            a, b, c = [-1*P[0][2]*self.Hpoly(0, 0, 2)(*pt) - P[0][0]*self.Gpoly(0, 2)(*pt),
                        - P[0][2]*self.Hpoly(0, 1, 2)(*pt) - P[0][1]*self.Gpoly(0, 2)(*pt),
                        P[0][2]*self.Gpoly(0, 2)(*pt)]
         Point = [a, b, c, P[1][0], P[1][1], P[1][2]]
-        if [a, b, c] != [0, 0, 0]:
+        if any([a, b, c]):
             if normalize:
                 Point = self.point(Point, False)
                 Point.normalize_coordinates()
@@ -1520,18 +1520,18 @@ def sigmaY(self, P, **kwds):
             if len(V) > 1:
                 raise ValueError("cannot distinguish points in the degenerate fiber")
             if len(V) == 1:
-                [a, b, c] = [V[0][z0], V[0][z1], V[0][z2]]
-            if len(V) == 0 or [a,b,c] == [0, 0, 0]:
+                a, b, c = [V[0][z0], V[0][z1], V[0][z2]]
+            if len(V) == 0 or not any([a, b, c]):
                 SS = PolynomialRing(BR, 3, 'z0, z1, z2', order='lex')
-                z0,z1,z2 = SS.gens()
+                z0, z1, z2 = SS.gens()
                 phi = RR.hom([1, 0, z0, z1, z2], SS)
                 J = phi(I)
                 if J.dimension() > 0:
                     raise ValueError("cannot distinguish points in the degenerate fiber")
                 V = phi(I).variety()
                 if len(V) > 1:
                     raise ValueError("cannot distinguish points in the degenerate fiber")
-                [a,b,c] = [V[0][z0], V[0][z1], V[0][z2]]
+                a, b, c = [V[0][z0], V[0][z1], V[0][z2]]
 
         Point = [a, b, c, P[1][0], P[1][1], P[1][2]]
         if normalize:

src/sage/geometry/hyperbolic_space/hyperbolic_geodesic.py

@@ -1213,11 +1213,10 @@ def ideal_endpoints(self):
             [Boundary point in UHP -sqrt(65) + 9,
              Boundary point in UHP sqrt(65) + 9]
         """
-
         start = self._start.coordinates()
         end = self._end.coordinates()
-        [x1, x2] = [real(k) for k in [start, end]]
-        [y1, y2] = [imag(k) for k in [start, end]]
+        x1, x2 = real(start), real(end)
+        y1, y2 = imag(start), imag(end)
         M = self._model
         # infinity is the first endpoint, so the other ideal endpoint
         # is just the real part of the second coordinate
@@ -2046,8 +2045,7 @@ def _to_std_geod(self, p):
             Full MatrixSpace of 2 by 2 dense matrices over Complex Field
             with 53 bits of precision
         """
-
-        [s, e] = [k.coordinates() for k in self.complete().endpoints()]
+        s, e = [k.coordinates() for k in self.complete().endpoints()]
         B = HyperbolicGeodesicUHP._get_B(p)
         # outmat below will be returned after we normalize the determinant.
         outmat = B * HyperbolicGeodesicUHP._crossratio_matrix(s, p, e)

src/sage/geometry/hyperbolic_space/hyperbolic_model.py

@@ -1091,9 +1091,9 @@ def random_isometry(self, preserve_orientation=True, **kwargs):
             sage: B.preserves_orientation()                                             # needs scipy
             False
         """
-        [a, b, c, d] = [RR.random_element() for k in range(4)]
+        a, b, c, d = [RR.random_element() for k in range(4)]
         while abs(a*d - b*c) < EPSILON:
-            [a, b, c, d] = [RR.random_element() for k in range(4)]
+            a, b, c, d = [RR.random_element() for k in range(4)]
         M = matrix(RDF, 2, [a, b, c, d])
         M = M / (M.det()).abs().sqrt()
         if M.det() > 0:

src/sage/graphs/graph.py

@@ -5787,7 +5787,7 @@ def write_to_eps(self, filename, **options):
         """
         from sage.graphs.print_graphs import print_graph_eps
         pos = self.layout(**options)
-        [xmin, xmax, ymin, ymax] = self._layout_bounding_box(pos)
+        xmin, xmax, ymin, ymax = self._layout_bounding_box(pos)
         for v in pos:
             pos[v] = (1.8*(pos[v][0] - xmin)/(xmax - xmin) - 0.9, 1.8*(pos[v][1] - ymin)/(ymax - ymin) - 0.9)
         if filename[-4:] != '.eps':

src/sage/graphs/graph_decompositions/graph_products.pyx

@@ -496,6 +496,7 @@ def rooted_product(G, H, root=None, immutable=None):
         raise ValueError("the specified root is not a vertex of H")
 
     vertices = ((u, x) for u in G for x in H)
+
     def edges():
         for u, v in G.edge_iterator(labels=False):
             yield ((u, root), (v, root))

src/sage/knots/link.py

@@ -2868,8 +2868,8 @@ def _bracket(self):
 
         cross = pd_code[0]
         rest = [list(vertex) for vertex in pd_code[1:]]
-        [a, b, c, d] = cross
-        if a == d and c == b and len(rest) > 0:
+        a, b, c, d = cross
+        if a == d and c == b and rest:
             return (~t + t**(-5)) * Link(rest)._bracket()
         elif a == b and c == d and len(rest) > 0:
             return (t + t**5) * Link(rest)._bracket()