Issue #25590: Make rlcompleter only call getattr() once per attribute

Previously it was called another time via hasattr(), and both calls were
made once for dir(f) and again for dir(f.__class__).  This includes a
backport of changing from a list to a set from revision 4dbb315fe667.

3 files changed, 26 insertions, 7 deletions

diff --git a/Lib/rlcompleter.py b/Lib/rlcompleter.py
index 6e4bd12ad3..73f8d80ee9 100644
--- a/Lib/rlcompleter.py
+++ b/Lib/rlcompleter.py
@@ -135,20 +135,23 @@ class Completer:
             return []
 
         # get the content of the object, except __builtins__
-        words = dir(thisobject)
-        if "__builtins__" in words:
-            words.remove("__builtins__")
+        words = set(dir(thisobject))
+        words.discard("__builtins__")
 
         if hasattr(thisobject, '__class__'):
-            words.append('__class__')
-            words.extend(get_class_members(thisobject.__class__))
+            words.add('__class__')
+            words.update(get_class_members(thisobject.__class__))
         matches = []
         n = len(attr)
         for word in words:
-            if word[:n] == attr and hasattr(thisobject, word):
-                val = getattr(thisobject, word)
+            if word[:n] == attr:
+                try:
+                    val = getattr(thisobject, word)
+                except Exception:
+                    continue  # Exclude properties that are not set
                 word = self._callable_postfix(val, "%s.%s" % (expr, word))
                 matches.append(word)
+        matches.sort()
         return matches
 
 def get_class_members(klass):
diff --git a/Lib/test/test_rlcompleter.py b/Lib/test/test_rlcompleter.py
index ac0e70dbcb..c969d278e4 100644
--- a/Lib/test/test_rlcompleter.py
+++ b/Lib/test/test_rlcompleter.py
@@ -65,6 +65,19 @@ class TestRlcompleter(unittest.TestCase):
                          ['egg.{}('.format(x) for x in dir(str)
                           if x.startswith('s')])
 
+    def test_excessive_getattr(self):
+        # Ensure getattr() is invoked no more than once per attribute
+        class Foo:
+            calls = 0
+            @property
+            def bar(self):
+                self.calls += 1
+                return None
+        f = Foo()
+        completer = rlcompleter.Completer(dict(f=f))
+        self.assertEqual(completer.complete('f.b', 0), 'f.bar')
+        self.assertEqual(f.calls, 1)
+
 def test_main():
     support.run_unittest(TestRlcompleter)
 
diff --git a/Misc/NEWS b/Misc/NEWS
index e9251039d2..43e0418b4d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -52,6 +52,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #25590: In the Readline completer, only call getattr() once per
+  attribute.
+
 - Issue #25530: Disable the vulnerable SSLv3 protocol by default when creating
   ssl.SSLContext.