gh-40916: more usage of enumerate()
    
as suggested by `ruff check --select=SIM113`

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #40916
Reported by: Frédéric Chapoton
Reviewer(s): Frédéric Chapoton, Martin Rubey

Author: Release Manager

src/sage/matrix/matrix_integer_dense_hnf.py

@@ -733,12 +733,10 @@ def ones(H, pivots):
     # that contain exactly one "1" entry and all other entries 0.
     onecol = []
     onerow = []
-    i = 0
-    for c in pivots:
+    for i, c in enumerate(pivots):
         if H[i, c] == 1:
             onecol.append(c)
             onerow.append(i)
-        i += 1
     onecol_set = set(onecol)
     non_onerow = [j for j in range(len(pivots)) if j not in onerow]
     non_onecol = [j for j in range(H.ncols()) if j not in onecol_set][:len(non_onerow)]

src/sage/matroids/constructor.py

@@ -928,11 +928,9 @@ def Matroid(groundset=None, data=None, **kwds):
             V = G.vertices(sort=True)
             n = G.num_verts()
             A = matrix(ZZ, n, m, 0)
-            mm = 0
-            for i, j, k in G.edge_iterator():
+            for mm, (i, j, k) in enumerate(G.edge_iterator()):
                 A[V.index(i), mm] = -1
                 A[V.index(j), mm] += 1  # So loops get 0
-                mm += 1
             M = RegularMatroid(matrix=A, groundset=groundset)
             want_regular = False  # Save some time, since result is already regular
         else:

src/sage/matroids/utilities.py

@@ -272,16 +272,8 @@ def make_regular_matroid_from_matroid(matroid):
     # First create a reduced 0-1 matrix
     B = list(M.basis())
     NB = list(M.groundset().difference(B))
-    dB = {}
-    i = 0
-    for e in B:
-        dB[e] = i
-        i += 1
-    dNB = {}
-    i = 0
-    for e in NB:
-        dNB[e] = i
-        i += 1
+    dB = {e: i for i, e in enumerate(B)}
+    dNB = {e: i for i, e in enumerate(NB)}
     A = Matrix(ZZ, len(B), len(NB), 0)
     G = BipartiteGraph(A.transpose())  # Sage's BipartiteGraph uses the column set as first color class. This is an edgeless graph.
     for e in NB:

src/sage/misc/latex.py

@@ -2164,45 +2164,36 @@ def repr_lincomb(symbols, coeffs):
         sage: latex(x)
         \text{\texttt{x}} + 2\text{\texttt{y}}
     """
-    s = ""
-    first = True
-    i = 0
-
     from sage.rings.cc import CC
+    terms = []
+    for c, sym in zip(coeffs, symbols):
+        if c == 0:
+            continue
+        if c == 1:
+            coeff = ""
+        elif c == -1:
+            coeff = "-"
+        else:
+            coeff = coeff_repr(c)
 
-    for c in coeffs:
-        bv = symbols[i]
-        b = latex(bv)
-        if c != 0:
-            if c == 1:
-                if first:
-                    s += b
-                else:
-                    s += " + %s" % b
+        b = latex(sym)
+        # this is a hack: I want to say that if the symbol happens to
+        # be a number, then we should put a multiplication sign in
+        try:
+            if sym in CC and coeff not in ("", "-"):
+                term = f"{coeff}\\cdot {b}"
             else:
-                coeff = coeff_repr(c)
-                if coeff == "-1":
-                    coeff = "-"
-                if first:
-                    coeff = str(coeff)
-                else:
-                    coeff = " + %s" % coeff
-                # this is a hack: i want to say that if the symbol
-                # happens to be a number, then we should put a
-                # multiplication sign in
-                try:
-                    if bv in CC:
-                        s += r"%s\cdot %s" % (coeff, b)
-                    else:
-                        s += "%s%s" % (coeff, b)
-                except Exception:
-                    s += "%s%s" % (coeff, b)
-            first = False
-        i += 1
-    if first:
-        s = "0"
-    s = s.replace("+ -", "- ")
-    return s
+                term = f"{coeff}{b}"
+        except Exception:
+            term = f"{coeff}{b}"
+
+        terms.append(term)
+
+    if not terms:
+        return "0"
+
+    s = " + ".join(terms)
+    return s.replace("+ -", "- ")
 
 
 common_varnames = ['alpha',

src/sage/monoids/automatic_semigroup.py

@@ -686,13 +686,11 @@ def _iter_concurrent(self):
             sage: M._constructed
             True
         """
-        i = 0
         # self._elements is never empty; so we are sure
-        for x in self._elements:
+        for i, x in enumerate(self._elements, 1):
             yield x
             # some other iterator/ method of the semigroup may have
             # been called before we move on to the next line
-            i += 1
             if i == len(self._elements) and not self._constructed:
                 try:
                     next(self._iter)

src/sage/rings/function_field/drinfeld_modules/charzero_drinfeld_module.py

@@ -626,10 +626,10 @@ def class_polynomial(self):
         # the Fq-vector space generated by the phi_T^i(T^(-s+1))
         # for i varying in NN.
         v = vector(Fq, s)
-        v[s-1] = 1
+        v[s - 1] = 1
         vs = [v]
-        for i in range(s-1):
-            v = v*M
+        for i in range(s - 1):
+            v = v * M
             vs.append(v)
         V = matrix(vs)
         V.echelonize()
@@ -638,12 +638,11 @@ def class_polynomial(self):
         # as an Fq-linear map (encoded in the matrix N)
         dim = V.rank()
         pivots = V.pivots()
-        j = ip = 0
-        for i in range(dim, s):
+        j = 0
+        for ip, i in enumerate(range(dim, s)):
             while ip < dim and j == pivots[ip]:
                 j += 1
-            ip += 1
-            V[i,j] = 1
+            V[i, j] = 1
         N = (V * M * ~V).submatrix(dim, dim)
 
         # The class module is now H where the action of T

src/sage/rings/number_field/number_field.py

@@ -11924,18 +11924,17 @@ def _multiplicative_order_table(self):
         try:
             return self.__multiplicative_order_table
         except AttributeError:
-            t = {}
-            x = self(1)
-            n = self.zeta_order()
-            m = 0
-            zeta = self.zeta(n)
-            # todo: this desperately needs to be optimized!!!
-            for i in range(n):
-                t[x.polynomial()] = n // gcd(m, n)  # multiplicative_order of (zeta_n)**m
-                x *= zeta
-                m += 1
-            self.__multiplicative_order_table = t
-            return t
+            pass
+        t = {}
+        x = self.one()
+        n = self.zeta_order()
+        zeta = self.zeta(n)
+        # todo: this desperately needs to be optimized!!!
+        for m in range(n):
+            t[x.polynomial()] = n // gcd(m, n)  # multiplicative_order of (zeta_n)**m
+            x *= zeta
+        self.__multiplicative_order_table = t
+        return t
 
     def zeta(self, n=None, all=False):
         """

src/sage/rings/polynomial/polynomial_quotient_ring.py

@@ -1351,13 +1351,10 @@ def _S_decomposition(self, S):
         fields = []
         isos = []
         iso_classes = []
-        i = 0
-        for f, _ in F:
-            D = K.extension(f, 'x'+str(i))
+        for i, (f, _) in enumerate(F):
+            D = K.extension(f, f'x{i}')
             fields.append(D)
-            D_abs = D.absolute_field('y'+str(i))
-            i += 1
-
+            D_abs = D.absolute_field(f'y{i}')
             seen_before = False
             j = 0
             for D_iso, _ in iso_classes:

src/sage/schemes/elliptic_curves/ell_egros.py

@@ -396,17 +396,15 @@ def egros_get_j(S=[], proof=None, verbose=False):
     SS = [-1] + S
 
     jlist = []
-    wcount = 0
     nw = 6**len(S) * 2
 
     if verbose:
         print("Finding possible j invariants for S = ", S)
         print("Using ", nw, " twists of base curve")
         sys.stdout.flush()
 
-    for ei in xmrange([6] * len(S) + [2]):
+    for wcount, ei in enumerate(xmrange([6] * len(S) + [2]), 1):
         w = QQ.prod(p**e for p, e in zip(reversed(SS), ei))
-        wcount += 1
         if verbose:
             print("Curve #", wcount, "/", nw, ":")
             print("w = ", w, "=", w.factor())

src/sage/schemes/elliptic_curves/ell_rational_field.py

@@ -6925,13 +6925,12 @@ def S_integral_x_coords_with_abs_bounded_by(abs_bound):
         mw_base_p_log = []
         beta = []
         mp = []
-        tmp = 0
-        for p in S:
+        for tmp, p in enumerate(S):
             Np = E.Np(p)
             cp = E.tamagawa_exponent(p)
             mp_temp = Z(len_tors).lcm(cp*Np)
             mp.append(mp_temp)  # only necessary because of verbose below
-            p_prec = 30+E.discriminant().valuation(p)
+            p_prec = 30 + E.discriminant().valuation(p)
             p_prec_ok = False
             while not p_prec_ok:
                 if verbose:
@@ -6957,7 +6956,6 @@ def S_integral_x_coords_with_abs_bounded_by(abs_bound):
             except ValueError:
                 # e.g. mw_base_p_log[tmp]==[0]:  can occur e.g. [?]'172c6, S=[2]
                 beta.append([0] for j in range(r))
-            tmp += 1
 
         if verbose:
             print('mw_base', mw_base)