fixing the ruff linter

Author: fchapoton

src/sage/combinat/abstract_tree.py

@@ -1478,7 +1478,7 @@ def node_to_str(t):
         while l_repr:
             tr = l_repr.pop(0)
             acc += UnicodeArt([" "]) + tr
-            if not len(l_repr):
+            if not l_repr:
                 lf_sep += "─" * (tr._root) + "╮"
                 ls_sep += " " * (tr._root) + "│"
             else:

src/sage/graphs/generators/smallgraphs.py

@@ -3337,7 +3337,7 @@ def pcycle(i, s):
             D.append(p)
         vv = 'q%s' % (int(p[1]) + 1)
         v = [v[-1] for v in H.neighbors(p) if v[:2] == vv]
-        if len(v):
+        if v:
             s = int(v[0])
         l += 1
     map = H.relabel(range(50), return_map=True)

src/sage/interfaces/axiom.py

@@ -843,7 +843,7 @@ def _sage_(self):
             return ZZ(repr(self))
         elif type.startswith('Polynomial'):
             from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
-            base_ring = P(type.lstrip('Polynomial '))._sage_domain()
+            base_ring = P(type.removeprefix('Polynomial '))._sage_domain()
             vars = str(self.variables())[1:-1]
             R = PolynomialRing(base_ring, vars)
             return R(self.unparsed_input_form())

src/sage/schemes/elliptic_curves/ell_finite_field.py

@@ -3179,7 +3179,7 @@ def abs_products_under(bound):
         """
         import heapq
         hq = [(1, 1, -1)]
-        while len(hq):
+        while hq:
             abs_n, n, idx = heapq.heappop(hq)
             yield n
             for nxt in range(idx + 1, len(S)):

src/sage/schemes/riemann_surfaces/riemann_surface.py

@@ -3869,8 +3869,8 @@ def divisor_to_divisor_list(self, divisor, eps=None):
                 ys = []
                 for gi in gis:
                     # This test is a bit clunky, it surely can be made more efficient.
-                    if len(ys):
-                        ers = min([gi(y, r).abs() for y in ys])
+                    if ys:
+                        ers = min(gi(y, r).abs() for y in ys)
                     else:
                         ers = 1
 

src/sage/topology/cubical_complex.py

@@ -1270,11 +1270,11 @@ def chain_complex(self, subcomplex=None, augmented=False,
                 # nonzero via a dictionary.
                 matrix_data = {}
                 col = 0
-                if len(old) and len(current):
+                if old and current:
                     for cube in current:
                         faces = cube.faces_as_pairs()
                         sign = 1
-                        for (upper, lower) in faces:
+                        for upper, lower in faces:
                             # trac 32203: use two "try/except" loops
                             # in case lower is in old but upper is not.
                             try: