src/sage/interfaces/maxima_abstract.py: clarify a comprehension

Using python's walrus operator we can simplify the list comprehension
that builds the list of maxima _commands(). Essentially this allows
us to save the result of foo.strip() and work with that rather than
the original unstripped string foo.

Author: orlitzky

src/sage/interfaces/maxima_abstract.py

@@ -344,10 +344,10 @@ def _commands(self):
         # with random leading spaces: ' tminverse', ' toeplitz', etc.
         #
         bad_chars = ("\\", "/", "?", "%")
-        return [c.strip()
-                for c in all_names
-                if c
-                and (c[0] in a_to_Z or c[0] == " ")
+        return [c
+                for n in all_names
+                if (c := n.strip())
+                and c[0] in a_to_Z
                 and not any(bad in c for bad in bad_chars)]
 
     def _tab_completion(self, verbose=True, use_disk_cache=True):