cython-lint for graphs/

[fchapoton]

fix many small details in pyx files in graphs, as found by

cython-lint --ignore=E501,E741,E265,E221,E231,E201,E127,E129 src/sage/graphs/

notably removing many unused def and variables.

There remains in particular a rather suspicious warning:

src/sage/graphs/distances_all_pairs.pyx:1977:9: 'ecc_antipode' defined but unused (try prefixing with underscore?)

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[github-actions]

Documentation preview for this PR (built with commit 4920ae7; changes) is ready! 🎉

[dcoudert]

LGTM.

[fchapoton]

merci. Quid du truc sur "ecc_antipode" défini mais pas utilisé ?

[dcoudert]

merci. Quid du truc sur "ecc_antipode" défini mais pas utilisé ?

Indeed, in file src/sage/graphs/distances_all_pairs.pyx, method radius_DHV, we can do:

diff --git a/src/sage/graphs/distances_all_pairs.pyx b/src/sage/graphs/distances_all_pairs.pyx
index a61fd4168a..412c1b51cb 100644
--- a/src/sage/graphs/distances_all_pairs.pyx
+++ b/src/sage/graphs/distances_all_pairs.pyx
@@ -1940,7 +1940,7 @@ def radius_DHV(G):
     init_short_digraph(sd, G, edge_labelled=False, vertex_list=int_to_vertex)
 
     cdef uint32_t source, ecc_source
-    cdef uint32_t antipode, ecc_antipode
+    cdef uint32_t antipode
     cdef uint32_t UB = UINT32_MAX
     cdef uint32_t LB = 0
 
@@ -1975,9 +1975,9 @@ def radius_DHV(G):
 
         # 2) Take vertex at largest distance from source, called antipode (last
         # vertex visited in simple_BFS), and compute its BFS distances.
-        # By definition of antipode, we have ecc_antipode >= ecc_source.
+        # By definition of antipode, we have ecc(antipode) >= ecc(source).
         antipode = waiting_list[n-1]
-        ecc_antipode = simple_BFS(sd, antipode, distances, NULL, waiting_list, seen)
+        _ = simple_BFS(sd, antipode, distances, NULL, waiting_list, seen)
 
         # 3) Use distances from antipode to improve eccentricity lower bounds.
         # We also determine the next source