gh-36854: various details in categories (ruff C4 and UP02)
    
fixing a few `ruff` suggestions in `categories` (UP02 and C4 ruff codes)

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
    
URL: #36854
Reported by: Frédéric Chapoton
Reviewer(s): Matthias Köppe

Author: Release Manager

src/sage/categories/aperiodic_semigroups.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Aperiodic semigroups
 """

src/sage/categories/cartesian_product.py

@@ -16,7 +16,7 @@
 from sage.categories.covariant_functorial_construction import CovariantFunctorialConstruction, CovariantConstructionCategory
 from sage.categories.pushout import MultivariateConstructionFunctor
 
-native_python_containers = set([tuple, list, set, frozenset, range])
+native_python_containers = {tuple, list, set, frozenset, range}
 
 class CartesianProductFunctor(CovariantFunctorialConstruction, MultivariateConstructionFunctor):
     """

src/sage/categories/category.py

@@ -2647,9 +2647,8 @@ def category_graph(categories=None):
         categories = category_sample()
     # Include all the super categories
     # Get rid of join categories
-    categories = set(cat
-                     for category in categories
-                     for cat in category.all_super_categories(proper=isinstance(category, JoinCategory)))
+    categories = {cat for category in categories
+                  for cat in category.all_super_categories(proper=isinstance(category, JoinCategory))}
     g = graphs.digraph.DiGraph()
     for cat in categories:
         g.add_vertex(cat._repr_object_names())
@@ -2859,7 +2858,7 @@ def _make_named_class_key(self, name):
              <class 'sage.categories.posets.Posets.element_class'>)
         """
 
-    _make_named_class_cache = dict()
+    _make_named_class_cache = {}
 
     _cmp_key = _cmp_key_named
 

src/sage/categories/commutative_rings.py

@@ -354,7 +354,7 @@ def cyclotomic_cosets(self, q, cosets=None):
                 if cosets is None:
                     rest = set(self)
                 else:
-                    rest = set(self(x) for x in cosets)
+                    rest = {self(x) for x in cosets}
 
                 orbits = []
                 while rest:

src/sage/categories/covariant_functorial_construction.py

@@ -145,7 +145,7 @@ def category_from_parents(self, parents):
         # But then this would impose that, for any constructor, the
         # category of the result does not depend on the order/repetition
         # of the categories of the parents
-        return self.category_from_categories(tuple(set(parent.category() for parent in parents)))
+        return self.category_from_categories(tuple({parent.category() for parent in parents}))
 
     @cached_method
     def category_from_categories(self, categories):

src/sage/categories/coxeter_groups.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Coxeter Groups
 """
@@ -633,8 +632,8 @@ class is not unique and we only obtain one such class.
             if not self.is_irreducible() or not self.is_well_generated():
                 raise ValueError("this method is available for irreducible, well-generated complex reflection groups")
             from sage.combinat.permutation import Permutations
-            return set(self.from_reduced_word(w)
-                       for w in Permutations(self.index_set()))
+            return {self.from_reduced_word(w)
+                    for w in Permutations(self.index_set())}
 
         def grassmannian_elements(self, side="right"):
             """
@@ -1061,7 +1060,7 @@ def bruhat_interval_poset(self, x, y, facade=False):
                 return Poset([[x], []])
             if not x.bruhat_le(y):
                 return Poset()
-            curlayer = set([y])
+            curlayer = {y}
             d = {}
             while curlayer:
                 nextlayer = set()
@@ -1263,8 +1262,8 @@ def _test_simple_projections(self, **options):
                         tester.assertEqual(opi[i](w), w.apply_simple_projection(i, side=side, length_increasing=False))
                         tester.assertTrue(pi[i](w).has_descent(i, side=side))
                         tester.assertFalse(opi[i](w).has_descent(i, side=side))
-                        tester.assertEqual(set([pi[i](w), opi[i](w)]),
-                                           set([w, w.apply_simple_reflection(i, side=side)]))
+                        tester.assertEqual({pi[i](w), opi[i](w)},
+                                           {w, w.apply_simple_reflection(i, side=side)})
 
         def _test_has_descent(self, **options):
             """

src/sage/categories/crystals.py

@@ -2082,7 +2082,7 @@ def __init__(self, parent, on_gens, cartan_type=None,
         elif isinstance(on_gens, collections.abc.Sequence):
             if len(self._gens) != len(on_gens):
                 raise ValueError("invalid generator images")
-            d = {x: y for x, y in zip(self._gens, on_gens)}
+            d = dict(zip(self._gens, on_gens))
             f = lambda x: d[x]
         else:
             f = on_gens
@@ -2239,7 +2239,7 @@ def to_module_generator(self, x):
             return self._path_mg_cache[x]
 
         mg = set(self._path_mg_cache.keys())
-        visited = set([None, x])
+        visited = {None, x}
         index_set = self._cartan_type.index_set()
         todo = [x]
         ef = [[]]

src/sage/categories/examples/commutative_additive_semigroups.py

@@ -164,8 +164,8 @@ def __init__(self, parent, iterable):
                 sage: x.value
                 {'a': 2, 'b': 0, 'c': 1, 'd': 5}
             """
-            d = dict( (a,0) for a in parent.alphabet )
-            for (a, c) in iterable:
+            d = {a: 0 for a in parent.alphabet}
+            for a, c in iterable:
                 d[a] = c
             ElementWrapper.__init__(self, parent, d)
 

src/sage/categories/examples/with_realizations.py

@@ -269,7 +269,7 @@ def supsets(self, set):
             [{1, 2, 3}, {2, 3}, {1, 2}, {2}]
         """
         S = self.base_set()
-        return list(S.difference(s) for s in Subsets(S.difference(set)))
+        return [S.difference(s) for s in Subsets(S.difference(set))]
 
     def _repr_(self):
         r"""

src/sage/categories/fields.py

@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 r"""
 Fields
 """