sagemathgh-39685: handling a few unused variables in geometry,graphs,numerical,structure
    
found using `cython-lint`

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: sagemath#39685
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager

src/sage/geometry/palp_normal_form.pyx

@@ -195,7 +195,7 @@ def _palp_PM_max(Matrix_integer_dense PM, check=False):
         else:
             S[i] = i + 1
 
-    cdef int l, np, cf, ccf, n_s_bar, d1, v0, vc, vj
+    cdef int l, cf, ccf, n_s_bar, d1, v0, vc, vj
     cdef list l_r
 
     # We determine the other rows of PM_max in turn by use of perms and

src/sage/graphs/base/static_sparse_graph.pyx

@@ -280,10 +280,9 @@ cdef int init_short_digraph(short_digraph g, G, edge_labelled=False,
     g.m = G.size()
 
     cdef int isdigraph = G.is_directed()
-    cdef uint32_t i, v_id, j
+    cdef uint32_t i, j
     cdef list vertices = vertex_list if vertex_list is not None else list(G)
     cdef dict v_to_id = {v: i for i, v in enumerate(vertices)}
-    cdef list neighbor_label
     cdef list edge_labels
     # Loops are not stored twice for undirected graphs
     cdef int n_edges = g.m if isdigraph else 2*g.m - G.number_of_loops()

src/sage/graphs/traversals.pyx

@@ -471,8 +471,6 @@ def lex_BFS(G, reverse=False, tree=False, initial_vertex=None, algorithm="fast")
     if algorithm != "fast":
         raise ValueError(f"unknown algorithm '{algorithm}'")
 
-    cdef size_t n = G.order()
-
     # For algorithm "fast" we need to convert G to an undirected graph
     if G.is_directed():
         G = G.to_undirected()
@@ -485,8 +483,6 @@ def lex_BFS(G, reverse=False, tree=False, initial_vertex=None, algorithm="fast")
     # Initialize variables needed by the fast algorithm
     cdef vector[int] sigma_int
     cdef vector[int] pred
-    # Initialize variables needed by the slow algorithm
-    cdef dict lexicographic_label
     # Temporary variables
     cdef int vi, i, initial_v_int
 
@@ -497,8 +493,8 @@ def lex_BFS(G, reverse=False, tree=False, initial_vertex=None, algorithm="fast")
     else:
         initial_v_int = -1
     extended_lex_BFS(cg, sigma_int, NULL, initial_v_int, &pred, NULL, NULL)
-    sigma = [ Gbackend.vertex_label(vi) for vi in sigma_int ]
-    predecessor = { u: sigma[i] for u, i in zip(sigma, pred) if i != -1 }
+    sigma = [Gbackend.vertex_label(vi) for vi in sigma_int]
+    predecessor = {u: sigma[i] for u, i in zip(sigma, pred) if i != -1}
 
     if reverse:
         sigma.reverse()

src/sage/numerical/backends/cvxopt_backend.pyx

@@ -300,7 +300,7 @@ cdef class CVXOPTBackend(GenericBackend):
         """
         for i in range(len(coeff)):
             self.objective_function[i] = coeff[i]
-        obj_constant_term = d
+        self.obj_constant_term = d
 
     cpdef set_verbosity(self, int level):
         """

src/sage/numerical/backends/matrix_sdp_backend.pyx

@@ -242,7 +242,7 @@ cdef class MatrixSDPBackend(GenericSDPBackend):
         """
         for i in range(len(coeff)):
             self.objective_function[i] = coeff[i]
-        obj_constant_term = d
+        self.obj_constant_term = d
 
     cpdef add_linear_constraint(self, coefficients, name=None):
         """

src/sage/numerical/mip.pyx

@@ -990,7 +990,6 @@ cdef class MixedIntegerLinearProgram(SageObject):
         """
         from sage.rings.integer import Integer as Integer
         cdef int i
-        cdef str s
         cdef GenericBackend b = self._backend
 
         result = []
@@ -1005,16 +1004,15 @@ cdef class MixedIntegerLinearProgram(SageObject):
             return (lb, b.row(indices), ub)
 
         # List of constraints
-        elif isinstance(indices, list):
+        if isinstance(indices, list):
             for i in indices:
                 lb, ub = b.row_bounds(i)
                 result.append((lb, b.row(i), ub))
 
             return result
 
         # Weird Input
-        else:
-            raise ValueError("constraints() requires a list of integers, though it will accommodate None or an integer.")
+        raise ValueError("constraints() requires a list of integers, though it will accommodate None or an integer.")
 
     def polyhedron(self, **kwds):
         r"""

src/sage/numerical/sdp.pyx

@@ -656,7 +656,7 @@ cdef class SemidefiniteProgram(SageObject):
 
         ##### Constraints
         print("Constraints:")
-        for 0<= i < b.nrows():
+        for i in range(b.nrows()):
             indices, values = b.row(i)
             print(" ", end=" ")
             # Constraint's name
@@ -666,7 +666,7 @@ cdef class SemidefiniteProgram(SageObject):
             l = sorted(zip(indices,values))
             l.reverse()
             if l[-1][0] == -1:
-                last_i,last_value = l.pop()
+                _, last_value = l.pop()
             else:
                 last_value = matrix.zero( l[0][1].dimensions()[0],l[0][1].dimensions()[1]  )
             l.reverse()

src/sage/structure/coerce.pyx

@@ -1600,7 +1600,7 @@ cdef class CoercionModel:
         """
         if homs is None:
             return None
-        cdef Map x_map, y_map
+        cdef Map R_map, S_map
         R_map, S_map = homs
         if isinstance(R, type):
             R = Set_PythonType(R)

src/sage/structure/coerce_actions.pyx

@@ -759,7 +759,7 @@ cdef class IntegerMulAction(IntegerAction):
     def __init__(self, Z, M, is_left=True, m=None):
         if m is None:
             m = M.an_element()
-        test = m + (-m)  # make sure addition and negation is allowed
+        _ = m + (-m)  # make sure addition and negation is allowed
         super().__init__(Z, M, is_left, operator.mul)
 
     cpdef _act_(self, nn, a):

src/sage/structure/element.pyx

@@ -712,7 +712,6 @@ cdef class Element(SageObject):
         """
         tester = self._tester(**options)
         SageObject._test_category(self, tester=tester)
-        category = self.category()
         # Tests that self inherits methods from the categories
         if can_assign_class(self):
             # For usual Python classes, that should be done with