bpo-32492: 1.6x speed up in namedtuple attribute access using C fast-path (#10495)

* bpo-32492: 2.5x speed up in namedtuple attribute access using C fast path

* Add News entry

* fixup! bpo-32492: 2.5x speed up in namedtuple attribute access using C fast path

* Check for tuple in the __get__ of the new descriptor and don't cache the descriptor itself

* Don't inherit from property. Implement GC methods to handle __doc__

* Add a test for the docstring substitution in descriptors

* Update NEWS entry to reflect time against 3.7 branch

* Simplify implementation with argument clinic, better error messages, only __new__

* Use positional-only parameters for the __new__

* Use PyTuple_GET_SIZE and PyTuple_GET_ITEM to tighter the implementation of tuplegetterdescr_get

* Implement __set__ to make tuplegetter a data descriptor

* Use Py_INCREF now that we inline PyTuple_GetItem

* Apply the valid_index() function, saving one test

* Move Py_None test out of the critical path.

1 files changed, 8 insertions, 0 deletions

diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index e2ffaaa..c081594 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -514,6 +514,14 @@ class TestNamedTuple(unittest.TestCase):
         a.w = 5
         self.assertEqual(a.__dict__, {'w': 5})
 
+    def test_namedtuple_can_mutate_doc_of_descriptors_independently(self):
+        A = namedtuple('A', 'x y')
+        B = namedtuple('B', 'x y')
+        A.x.__doc__ = 'foo'
+        B.x.__doc__ = 'bar'
+        self.assertEqual(A.x.__doc__, 'foo')
+        self.assertEqual(B.x.__doc__, 'bar')
+
 
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 ### Abstract Base Classes