gh-39305: fixing some ruff PLR warnings

    
here about useless return at the end of functions and methods

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #39305
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

src/sage/algebras/hecke_algebras/cubic_hecke_algebra.py

@@ -1116,7 +1116,6 @@ def check_base_ring_embedding(base_ring_embedding):
         # initializing the basis extension (in case of more than 4 strands)
         # ----------------------------------------------------------------------
         self._init_basis_extension()
-        return
 
     ############################################################################
     # --------------------------------------------------------------------------

src/sage/algebras/hecke_algebras/cubic_hecke_base_ring.py

@@ -105,8 +105,6 @@ def register_ring_hom(ring_hom):
         except ValueError:
             verbose('\nthe map:\n%s\ncannot be registered as conversion\n' % ring_hom)
 
-    return
-
 
 # -----------------------------------------------------------------------------
 # class for the Galois Group action on the generic extension ring corresponding
@@ -1005,11 +1003,10 @@ def __init__(self, names=('u', 'v', 'w', 's'), order='degrevlex', markov_trace_v
         # Init of data used on demand
         # ----------------------------------------------------------------------
         self._mirror = None
-        return
 
-    ############################################################################
+    # ########################################################################
     # overloaded inherited methods
-    ############################################################################
+    # ########################################################################
     def _defining_names(self):
         r"""
         Return the generators of ``self`` as the defining names.

src/sage/categories/affine_weyl_groups.py

@@ -130,7 +130,7 @@ def succ(pair):
                     if (length < k and i == u1.first_descent(side='left') and
                             u1.is_affine_grassmannian()):
                         yield (u1, length + 1)
-                return
+
             return RecursivelyEnumeratedSet_forest(((self.one(), 0),), succ, algorithm='breadth',
                                                    category=FiniteEnumeratedSets(),
                                                    post_process=select_length)

src/sage/combinat/diagram_algebras.py

@@ -4795,7 +4795,7 @@ def insert_pairing(cur, intervals):
                 # Singleton intervals are vertical lines,
                 #   so we don't need to worry about them
                 if len(I) > 1 and I[0] < cur[0]:
-                    cur, level[j] = level[j], cur
+                    cur, level[j] = I, cur
                     level.append([cur[0]])
                     level.append([cur[1]])
                     break

src/sage/combinat/necklace.py

@@ -360,12 +360,11 @@ def _fast_fixed_content(a, content, t, p, k, r, s, dll, equality=False):
             content[j] += 1
             j = dll.next(j)
         a[t - 1] = k - 1
-    return
 
 
-################################
-# List Fixed Content Algorithm #
-################################
+# ###############################
+# List Fixed Content Algorithm  #
+# ###############################
 def _lfc(content, equality=False):
     """
     EXAMPLES::

src/sage/combinat/non_decreasing_parking_function.py

@@ -629,6 +629,5 @@ def iterator_rec(n):
             return
         for res in iterator_rec(self.n):
             yield NonDecreasingParkingFunction(res)
-        return
 
     Element = NonDecreasingParkingFunction

src/sage/combinat/tableau.py

@@ -8133,8 +8133,6 @@ def __iter__(self):
 
             yield self.element_class(self, tableau)
 
-        return
-
     def list(self):
         r"""
         Return a list of the standard Young tableaux of the specified shape.

src/sage/combinat/tableau_tuple.py

@@ -4926,7 +4926,6 @@ def max_row_in_component(tab, r):
             yield tableau_from_list(tab)
 
         # all done!
-        return
 
     def last(self):
         r"""

src/sage/combinat/words/suffix_trees.py

@@ -501,7 +501,6 @@ def show(self, *args, **kwds):
             sage: t.show()                                                              # needs sage.plot
         """
         self.plot(*args, **kwds).show()
-        return
 
 ################################################################################
 # Suffix Trees
@@ -656,7 +655,6 @@ def _process_letter(self, letter):
         # set the active state
         s, k = self._canonize(s, (k, i))
         self._active_state = (s, (k, i+1))
-        return
 
     def _test_and_split(self, s, k_p, letter):
         r"""
@@ -918,7 +916,6 @@ def show(self, word_labels=None, *args, **kwds):
             sage: t.show(word_labels=False)                                             # needs sage.plot
         """
         self.plot(word_labels=word_labels, *args, **kwds).show()
-        return
 
     #####
     # Various methods
@@ -1115,7 +1112,6 @@ def to_explicit_suffix_tree(self):
             end_state, r = self._test_and_split(s, (k, i-1), end_of_string)
         # remove the end of string symbol from the word
         self._letters.pop()
-        return
 
     def edge_iterator(self):
         r"""

src/sage/databases/cubic_hecke_db.py

@@ -1153,7 +1153,6 @@ def update_basis_extensions(self, new_basis_extensions):
         """
         self._data_library.update({self.section.basis_extensions: new_basis_extensions})
         self.write(self.section.basis_extensions)
-        return
 
 
 # -----------------------------------------------------------------------------

src/sage/graphs/bipartite_graph.py

@@ -1070,7 +1070,6 @@ def add_edge(self, u, v=None, label=None):
 
         # add the edge
         Graph.add_edge(self, u, v, label)
-        return
 
     def add_edges(self, edges, loops=True):
         """

src/sage/graphs/matching_covered_graph.py

@@ -2661,8 +2661,6 @@ def remove_loops(self, vertices=None):
             raise TypeError(f'\'{vertices.__class__.__name__}\' '
                             'object is not iterable')
 
-        return
-
     @doc_index('Miscellaneous methods')
     def update_matching(self, matching):
         r"""

src/sage/groups/cubic_braid.py

@@ -801,7 +801,6 @@ def __init__(self, names, cbg_type=None):
         self._classical_embedding = None   # if self._classical_group different from self._classical_base_group
         self._centralizing_matrix = None   # for Assion groups: element in classical base group commuting with self
         self._centralizing_element = None   # image under nat. map of the former one in the proj. classical group
-        return
 
     def _repr_(self):
         r"""
@@ -913,7 +912,6 @@ def _internal_test_attached_group(self, attached_group, tester):
         if self.is_finite() and self.strands() <= 7: # not realistic for larger number of strands
             att_grp_elem_back = self(att_grp_elem)
             tester.assertEqual(att_grp_elem_back, elem)
-        return
 
     def _test_classical_group(self, **options):
         r"""
@@ -934,7 +932,6 @@ def _test_classical_group(self, **options):
         classic_grp = self.as_classical_group()
         if self.is_finite():
             self._internal_test_attached_group(classic_grp, tester)
-        return
 
     def _test_permutation_group(self, **options):
         r"""
@@ -955,7 +952,6 @@ def _test_permutation_group(self, **options):
             tester = self._tester(**options)
             permgrp = self.as_permutation_group()
             self._internal_test_attached_group(permgrp, tester)
-        return
 
     def _test_matrix_group(self, **options):
         r"""
@@ -1024,7 +1020,6 @@ def _test_reflection_group(self, **options):
                 tester = self._tester(**options)
                 reflgrp = self.as_reflection_group()
                 self._internal_test_attached_group(reflgrp, tester)
-        return
 
     # -------------------------------------------------------------------------------
     # -------------------------------------------------------------------------------
@@ -1135,7 +1130,6 @@ def set_classical_realization(self, base_group, proj_group, centralizing_matrix,
             self._centralizing_matrix = centralizing_matrix
             self._centralizing_element = centralizing_element
             self._classical_embedding = embedding
-            return
 
         # -------------------------------------------------------------------------------
         # local methods to set up the classical group (specific part)
@@ -1210,7 +1204,6 @@ def transvec2mat(v, bas=bas, bform=bform, fact=1):
             transvec_matrices = [transvec2mat(v) for v in transvections]
 
             set_classical_realization(self, base_group, proj_group, centralizing_matrix, transvec_matrices)
-            return
 
         # -------------------------------------------------------------------------------
         # Case for unitary groups
@@ -1295,7 +1288,6 @@ def transvec2mat(v, bas=bas, bform=bform, fact=a):
             transvec_matrices = [transvec2mat(v) for v in transvections]
 
             set_classical_realization(self, base_group, proj_group, centralizing_matrix, transvec_matrices)
-            return
 
         # ----------------------------------------------------------------
         # local functions declaration section finishes here
@@ -1346,7 +1338,6 @@ def transvec2mat(v, bas=bas, bform=bform, fact=a):
             self._classical_embedding = classical_group
             if self._classical_invariant_form is None:
                 self._classical_invariant_form = classical_group.ambient().invariant_form()
-        return
 
     def _element_constructor_(self, x, **kwds):
         r"""

src/sage/interfaces/octave.py

@@ -351,7 +351,6 @@ def quit(self, verbose=False):
         if self._expect is not None:
             if verbose:
                 print("Exiting spawned %s process." % self)
-        return
 
     def _start(self):
         """

src/sage/lfunctions/dokchitser.py

@@ -287,7 +287,6 @@ def _instantiate_gp(cls):
 
         cls.__globals_re = re.compile(
             '([^a-zA-Z0-9_]|^)(%s)([^a-zA-Z0-9_]|$)' % '|'.join(cls.__globals))
-        return
 
     @classmethod
     def _teardown_gp(cls, instance=None):

src/sage/matrix/operation_table.py

@@ -777,7 +777,6 @@ def set_print_symbols(self, ascii, latex):
             raise ValueError('LaTeX symbol must be a string, not %s' % latex)
         self._ascii_symbol = ascii
         self._latex_symbol = latex
-        return None
 
     def column_keys(self):
         r"""
@@ -931,7 +930,6 @@ def change_names(self, names):
             (1,2)
         """
         self._width, self._names, self._name_dict = self._name_maker(names)
-        return None
 
     def matrix_of_variables(self):
         r"""

src/sage/matroids/utilities.py

@@ -792,7 +792,6 @@ def split_vertex(G, u, v=None, edges=None):
         G.delete_edge(e)
 
     # This modifies the graph without needing to return anything
-    return
 
 
 def cmp_elements_key(x):

src/sage/plot/hyperbolic_arc.py

@@ -167,7 +167,6 @@ def _bezier_path(self, z0, z1, model, first=False):
                     self.path.append(points[N: N + 3])
                     N += 3
                 self.last_plotted = "arc"
-        return
 
 
 class HyperbolicArc(HyperbolicArcCore):

src/sage/quadratic_forms/quadratic_form__neighbors.py

@@ -327,7 +327,7 @@ def neighbor_iteration(seeds, p, mass=None, max_classes=None,
         def p_divisible_vectors(Q, max_neighbors):
             yield from iter(v.lift() for v in Q.orbits_lines_mod_p(p)
                             if v != 0 and Q(v.lift()).valuation(p) > 0)
-            return
+
     elif algorithm == 'exhaustion':
         def p_divisible_vectors(Q, max_neighbors):
             k = 0

src/sage/rings/lazy_series.py

@@ -4948,7 +4948,6 @@ def compute_coefficients(self, i):
         """
         from sage.misc.superseded import deprecation
         deprecation(32367, "the method compute_coefficients obsolete and has no effect.")
-        return
 
     def _im_gens_(self, codomain, im_gens, base_map=None):
         """

src/sage/rings/tests.py

@@ -501,4 +501,3 @@ def test_karatsuba_multiplication(base_ring, maxdeg1, maxdeg2,
             msg += "and\n"
             msg += f"{sage_input(g)}"
             raise ValueError(msg)
-    return