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gh-94155: Reduce hash collisions for code objects (#100183)

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* Uses a better hashing algorithm to get better dispersion and remove commutativity.

* Incorporates `co_firstlineno`, `Py_SIZE(co)`, and bytecode instructions.

* This is now the entire set of criteria used in `code_richcompare`, except for `_PyCode_ConstantKey` (which would incorporate the types of `co_consts` rather than just their values).
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Dennis Sweeney 2022-12-23 13:15:47 -05:00 • committed by GitHub
parent 36d358348d
commit a98d9ea56e
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3 changed files with 60 additions and 20 deletions
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26
Lib/test/test_code.py
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@ -465,6 +465,32 @@ class CodeTest(unittest.TestCase):
self.assertNotEqual(code_b, code_d)
self.assertNotEqual(code_c, code_d)
def test_code_hash_uses_firstlineno(self):
c1 = (lambda: 1).__code__
c2 = (lambda: 1).__code__
self.assertNotEqual(c1, c2)
self.assertNotEqual(hash(c1), hash(c2))
c3 = c1.replace(co_firstlineno=17)
self.assertNotEqual(c1, c3)
self.assertNotEqual(hash(c1), hash(c3))
def test_code_hash_uses_order(self):
# Swapping posonlyargcount and kwonlyargcount should change the hash.
c = (lambda x, y, *, z=1, w=1: 1).__code__
self.assertEqual(c.co_argcount, 2)
self.assertEqual(c.co_posonlyargcount, 0)
self.assertEqual(c.co_kwonlyargcount, 2)
swapped = c.replace(co_posonlyargcount=2, co_kwonlyargcount=0)
self.assertNotEqual(c, swapped)
self.assertNotEqual(hash(c), hash(swapped))
def test_code_hash_uses_bytecode(self):
c = (lambda x, y: x + y).__code__
d = (lambda x, y: x * y).__code__
c1 = c.replace(co_code=d.co_code)
self.assertNotEqual(c, c1)
self.assertNotEqual(hash(c), hash(c1))
def isinterned(s):
return s is sys.intern(('_' + s + '_')[1:-1])