Rewrite loop computing outside corners

src/sage/combinat/partition.py

@@ -4030,12 +4030,9 @@ def outside_corners(self):
         p = self
         if p.is_empty():
             return [(0,0)]
-        res = [ (0, p[0]) ]
-        for i in range(1, len(p)):
-            if p[i-1] != p[i]:
-                res.append((i,p[i]))
+        res = [(0, p[0])]
+        res.extend((n, j) for n, (i, j) in enumerate(zip(p[:-1], p[1:]), start=1) if i != j)
         res.append((len(p), 0))
-
         return res
 
     addable_cells = outside_corners   # for compatibility with partition tuples