sagemathgh-38635: fixing most ruff PERF4 warnings in combinat

    
this is fixing most suggestions of `ruff check --select=PERF4` in the
combinat folder.

### 📝 Checklist

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- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
    
URL: sagemath#38635
Reported by: Frédéric Chapoton
Reviewer(s): Matthias Köppe

src/sage/combinat/composition_tableau.py

@@ -211,10 +211,7 @@ def descent_set(self):
             sage: CompositionTableau([[1],[3,2],[4,4]]).descent_set()
             [1, 3]
         """
-        cols = {}
-        for row in self:
-            for col, i in enumerate(row):
-                cols[i] = col
+        cols = {i: col for row in self for col, i in enumerate(row)}
         return sorted(i for i in cols if i + 1 in cols and cols[i + 1] >= cols[i])
 
     def descent_composition(self):

src/sage/combinat/diagram.py

@@ -336,12 +336,9 @@ def _latex_(self):
 
         lr = r'\def\lr#1{\multicolumn{1}{|@{\hspace{.6ex}}c@{\hspace{.6ex}}|}{\raisebox{-.3ex}{$#1$}}}'
 
-        array = []
-        for i in range(self._n_rows):
-            row = []
-            for j in range(self._n_cols):
-                row.append("\\phantom{x}" if (i, j) in self else None)
-            array.append(row)
+        array = [[("\\phantom{x}" if (i, j) in self else None)
+                  for j in range(self._n_cols)]
+                 for i in range(self._n_rows)]
 
         def end_line(r):
             # give the line ending to row ``r``

src/sage/combinat/diagram_algebras.py

@@ -3013,7 +3013,7 @@ def jucys_murphy_element(self, i):
             sage: L = [P.L(i/2) for i in range(1,2*k+1)]
             sage: all(x.dual() == x for x in L)
             True
-            sage: all(x * y == y * x for x in L for y in L)  # long time
+            sage: all(x * y == y * x for x, y in Subsets(L, 2))  # long time
             True
             sage: Lsum = sum(L)
             sage: gens = [P.s(i) for i in range(1,k)]
@@ -3045,13 +3045,13 @@ def jucys_murphy_element(self, i):
 
         The same tests for a half integer partition algebra::
 
-            sage: k = 9/2
+            sage: k = 7/2
             sage: R.<n> = QQ[]
             sage: P = PartitionAlgebra(k, n)
             sage: L = [P.L(i/2) for i in range(1,2*k+1)]
             sage: all(x.dual() == x for x in L)
             True
-            sage: all(x * y == y * x for x in L for y in L)  # long time
+            sage: all(x * y == y * x for x, y in Subsets(L, 2))  # long time
             True
             sage: Lsum = sum(L)
             sage: gens = [P.s(i) for i in range(1,k-1/2)]
@@ -5847,11 +5847,9 @@ def to_Brauer_partition(l, k=None):
         True
     """
     L = to_set_partition(l, k=k)
-    L2 = []
     paired = []
     not_paired = []
-    for i in L:
-        L2.append(list(i))
+    L2 = (list(i) for i in L)
     for i in L2:
         if len(i) > 2:
             raise ValueError("blocks must have size at most 2, but {} has {}".format(i, len(i)))

src/sage/combinat/dlx.py

@@ -484,10 +484,7 @@ def AllExactCovers(M):
     ones = []
     r = 1    # damn 1-indexing
     for R in M.rows():
-        row = []
-        for i in range(len(R)):
-            if R[i]:
-                row.append(i + 1)  # damn 1-indexing
+        row = [i for i, Ri in enumerate(R, start=1) if Ri]
         ones.append([r, row])
         r += 1
     for s in DLXMatrix(ones):

src/sage/combinat/finite_state_machine.py

@@ -9437,9 +9437,9 @@ def graph(self, edge_labels='words_in_out'):
             transitions = state.transitions
             if not transitions:
                 isolated_vertices.append(state.label())
-            for t in transitions:
-                graph_data.append((t.from_state.label(), t.to_state.label(),
-                                   label_fct(t)))
+            graph_data.extend((t.from_state.label(), t.to_state.label(),
+                               label_fct(t))
+                              for t in transitions)
 
         G = DiGraph(graph_data, multiedges=True, loops=True)
         G.add_vertices(isolated_vertices)

src/sage/combinat/free_dendriform_algebra.py

@@ -939,14 +939,12 @@ def merge(self, other):
                 return self
             ret = list(self.vars)
             cur_vars = set(ret)
-            for v in other.vars:
-                if v not in cur_vars:
-                    ret.append(v)
+            ret.extend(v for v in other.vars if v not in cur_vars)
             return DendriformFunctor(Alphabet(ret))
-        else:
-            return None
 
-    def _repr_(self):
+        return None
+
+    def _repr_(self) -> str:
         """
         TESTS::
 

src/sage/combinat/free_prelie_algebra.py

@@ -1023,14 +1023,12 @@ def merge(self, other):
                 return self
             ret = list(self.vars)
             cur_vars = set(ret)
-            for v in other.vars:
-                if v not in cur_vars:
-                    ret.append(v)
+            ret.extend(v for v in other.vars if v not in cur_vars)
             return PreLieFunctor(Alphabet(ret))
-        else:
-            return None
 
-    def _repr_(self):
+        return None
+
+    def _repr_(self) -> str:
         """
         TESTS::
 

src/sage/combinat/gelfand_tsetlin_patterns.py

@@ -302,11 +302,9 @@ def boxed_entries(self) -> tuple:
             sage: G.boxed_entries()
             ((1, 0),)
         """
-        ret = []
-        for i in range(1, len(self)):
-            for j in range(len(self[i])):
-                if self[i][j] == self[i - 1][j]:
-                    ret.append((i, j))
+        ret = [(i, j) for i in range(1, len(self))
+               for j, selfij in enumerate(self[i])
+               if selfij == self[i - 1][j]]
         return tuple(ret)
 
     @cached_method
@@ -324,11 +322,9 @@ def circled_entries(self) -> tuple:
             sage: G.circled_entries()
             ((1, 1), (2, 0))
         """
-        ret = []
-        for i in range(1, len(self)):
-            for j in range(len(self[i])):
-                if self[i][j] == self[i - 1][j + 1]:
-                    ret.append((i, j))
+        ret = [(i, j) for i in range(1, len(self))
+               for j, selfij in enumerate(self[i])
+               if selfij == self[i - 1][j + 1]]
         return tuple(ret)
 
     @cached_method
@@ -349,11 +345,9 @@ def special_entries(self) -> tuple:
             sage: G.special_entries()
             ((2, 0),)
         """
-        ret = []
-        for i in range(1, len(self)):
-            for j in range(len(self[i])):
-                if self[i-1][j] > self[i][j] and self[i][j] > self[i-1][j+1]:
-                    ret.append((i, j))
+        ret = [(i, j) for i in range(1, len(self))
+               for j, selfij in enumerate(self[i])
+               if self[i - 1][j] > selfij > self[i - 1][j + 1]]
         return tuple(ret)
 
     def number_of_boxes(self) -> int:

src/sage/combinat/graph_path.py

@@ -236,11 +236,7 @@ def paths_from_source_to_target(self, source, target):
             [[2, 3, 4], [2, 4]]
         """
         source_paths = self.outgoing_paths(source)
-        paths = []
-        for path in source_paths:
-            if path[-1] == target:
-                paths.append(path)
-        return paths
+        return [path for path in source_paths if path[-1] == target]
 
     def paths(self):
         """

src/sage/combinat/integer_vector.py

@@ -1174,19 +1174,17 @@ def _list_rec(self, n, k):
         EXAMPLES::
 
             sage: IV = IntegerVectors(2,3)
-            sage: IV._list_rec(2,3)
+            sage: list(IV._list_rec(2,3))
             [(2, 0, 0), (1, 1, 0), (1, 0, 1), (0, 2, 0), (0, 1, 1), (0, 0, 2)]
         """
-        res = []
-
         if k == 1:
-            return [(n, )]
+            yield (n,)
+            return
 
         for nbar in range(n + 1):
             n_diff = n - nbar
             for rest in self._list_rec(nbar, k - 1):
-                res.append((n_diff,) + rest)
-        return res
+                yield (n_diff,) + rest
 
     def __iter__(self):
         """

src/sage/combinat/knutson_tao_puzzles.py

@@ -2064,12 +2064,9 @@ def _fill_piece(self, nw_label, ne_label, pieces) -> list[PuzzlePiece]:
             sage: ps._fill_piece('0', '0', ps._bottom_deltas)
             [0/0\0]
         """
-        output = []
-        for piece in pieces:
-            if (piece['north_west'] == nw_label and
-                    piece['north_east'] == ne_label):
-                output.append(piece)
-        return output
+        return [piece for piece in pieces
+                if (piece['north_west'] == nw_label and
+                    piece['north_east'] == ne_label)]
 
     @cached_method
     def _fill_strip(self, nw_labels, ne_label, pieces, final_pieces=None):

src/sage/combinat/misc.py

@@ -202,11 +202,7 @@ def _monomial_exponent_to_lower_factorial(me, x):
         sage: _monomial_exponent_to_lower_factorial(([2,2,2]),a)
         x^2*y^2*z^2 - x^2*y^2*z - x^2*y*z^2 - x*y^2*z^2 + x^2*y*z + x*y^2*z + x*y*z^2 - x*y*z
     """
-    terms = []
-    for i in range(len(me)):
-        for j in range(me[i]):
-            terms.append( x[i]-j )
-    return prod(terms)
+    return prod(x[i] - j for i, mei in enumerate(me) for j in range(mei))
 
 
 def umbral_operation(poly):
@@ -235,7 +231,7 @@ def umbral_operation(poly):
     exponents = poly.exponents()
     coefficients = poly.coefficients()
     length = len(exponents)
-    return sum( [coefficients[i]*_monomial_exponent_to_lower_factorial(exponents[i],x) for i in range(length)] )
+    return sum(coefficients[i]*_monomial_exponent_to_lower_factorial(exponents[i], x) for i in range(length))
 
 
 class IterableFunctionCall:

src/sage/combinat/parallelogram_polyomino.py

@@ -1974,12 +1974,9 @@ def widths(self) -> list:
             sage: pp.widths()
             []
         """
-        widths = []
         uw = self.upper_widths()
         lw = self.lower_widths()
-        for i in range(len(lw)):
-            widths.append(uw[i] - lw[i])
-        return widths
+        return [up - lo for up, lo in zip(uw, lw)]
 
     def degree_convexity(self) -> int:
         r"""
@@ -3387,11 +3384,10 @@ def get_BS_nodes(self):
             sage: pp.set_options(drawing_components=dict(tree=True))
             sage: view(pp) # not tested
         """
-        result = []
-        for h in range(1, self.height()):
-            result.append(self._get_node_position_at_row(h))
-        for w in range(1, self.width()):
-            result.append(self._get_node_position_at_column(w))
+        result = [self._get_node_position_at_row(h)
+                  for h in range(1, self.height())]
+        result.extend(self._get_node_position_at_column(w)
+                      for w in range(1, self.width()))
         return result
 
     def get_right_BS_nodes(self):

src/sage/combinat/partition_algebra.py

@@ -364,9 +364,7 @@ def __iter__(self):
             True
         """
         for p in Permutations(self.k):
-            res = []
-            for i in range(self.k):
-                res.append(Set([i + 1, -p[i]]))
+            res = [Set([i, -pi]) for i, pi in enumerate(p, start=1)]
             yield self.element_class(self, res)
 
 
@@ -433,10 +431,7 @@ def __iter__(self):
              {{1, -3}, {2, -2}, {4, -4}, {3, -1}}]
         """
         for p in Permutations(self.k):
-            res = []
-            for i in range(self.k):
-                res.append(Set([i + 1, -p[i]]))
-
+            res = [Set([i, -pi]) for i, pi in enumerate(p, start=1)]
             res.append(Set([self.k + 1, -self.k - 1]))
             yield self.element_class(self, res)
 
@@ -1941,8 +1936,8 @@ def to_set_partition(l, k=None):
         to_be_added -= spart
         sp.append(spart)
 
-    for singleton in to_be_added:
-        sp.append(Set([singleton]))
+    sp.extend(Set([singleton])
+              for singleton in to_be_added)
 
     return Set(sp)
 

src/sage/combinat/ribbon_shaped_tableau.py

@@ -350,18 +350,17 @@ def from_permutation(self, p):
              [[1, 2], [3]],
              [[1], [2], [3]]]
         """
-        if p == []:
+        if not p:
             return self.element_class(self, [])
 
         comp = p.descents()
 
-        if comp == []:
+        if not comp:
             return self.element_class(self, [p[:]])
 
-        r = []
-        r.append([p[j] for j in range(comp[0])])
-        for i in range(len(comp) - 1):
-            r.append([p[j] for j in range(comp[i], comp[i + 1])])
+        r = [[p[j] for j in range(comp[0])]]
+        r.extend([p[j] for j in range(comp[i], comp[i + 1])]
+                 for i in range(len(comp) - 1))
         r.append([p[j] for j in range(comp[-1], len(p))])
         r.reverse()
         return self.element_class(self, r)

src/sage/combinat/rsk.py

@@ -2957,12 +2957,10 @@ def _backward_format_output(self, obj1, obj2, output):
                 if j == 0:
                     df.append([])
                 if j > 0 and obj1[j] < obj1[j-1]:
-                    for _ in range(obj1[j-1]-obj1[j]):
-                        df.append([])
+                    df.extend([] for _ in range(obj1[j-1]-obj1[j]))
                 df[-1].append(obj2[j])
             if obj1:
-                for a in range(obj1[-1]-1):
-                    df.append([])
+                df.extend([] for a in range(obj1[-1]-1))
             # If biword is empty, return a decreasing factorization with 1 factor
             else:
                 df.append([])

src/sage/combinat/shifted_primed_tableau.py

@@ -2716,9 +2716,11 @@ def _add_strip(sub_tab, full_tab, length):
             if sub_tab and len(sub_tab) < len(full_tab):
                 plat_list.append(min(sub_tab[-1] + primed_strip[-2] - 1,
                                      full_tab[len(sub_tab)]))
-            for row in reversed(range(1, len(sub_tab))):
-                plat_list.append(min(sub_tab[row-1]+primed_strip[row-1]-1, full_tab[row])
-                                 - sub_tab[row] - primed_strip[row])
+            plat_list.extend(
+                min(sub_tab[row-1] + primed_strip[row-1] - 1, full_tab[row])
+                - sub_tab[row] - primed_strip[row]
+                for row in reversed(range(1, len(sub_tab))))
+
             if sub_tab:
                 plat_list.append(full_tab[0] - sub_tab[0] - primed_strip[0])
             else: