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add a small test for hashability of bare classes #296

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4d5a7eb
add a small test for hashability of bare classes
matthiasdiener Apr 3, 2025
43cea0b
Merge branch 'main' into test-bare-class
matthiasdiener Jun 18, 2025
e35c58a
fix local classes
matthiasdiener Jun 18, 2025
a722191
bpr
matthiasdiener Jun 18, 2025
b30b29e
disable local-class hashing
matthiasdiener Jun 18, 2025
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10 changes: 10 additions & 0 deletions pytools/test/test_persistent_dict.py
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Expand Up @@ -528,6 +528,16 @@ def update_persistent_hash(self, key_hash, key_builder):
def test_class_hashing() -> None:
keyb = KeyBuilder()

class WithoutUpdateMethod:
pass

assert keyb(WithoutUpdateMethod) == keyb(WithoutUpdateMethod)

@inducer inducer Jun 7, 2025

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Arguably, this should not work. This is a different class every time the function gets called. It might be useful to see if the class type has the same id() as the one available at the advertised name, before using that name for hashing.

@matthiasdiener matthiasdiener Jun 9, 2025

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Hmm, I'm not sure I understand. Do you mean, every time test_class_hashing is called, the class is different? But this isn't really tested in this line, perhaps more like in the next line assert keyb(WithoutUpdateMethod) == "da060d601d180d4c"?

@inducer inducer Jun 18, 2025

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Do you mean, every time test_class_hashing is called, the class is different?

Yes.

My point is that a function-local class does not have a globally valid name and thus should not be hashable. This can be tested by attempting to import it by its __qualname__ (won't work for local classes) and seeing if it comes back with the same id (just to be safe).

@matthiasdiener matthiasdiener Jun 18, 2025

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TIL, thanks! What do you think of e35c58a? I'm worried that this may cause extra cache misses since some tags that we use might be local classes?

assert keyb(WithoutUpdateMethod) == "da060d601d180d4c"

with pytest.raises(TypeError):
# does not have update_persistent_hash() = > will raise
keyb(WithoutUpdateMethod())

class WithUpdateMethod:
def update_persistent_hash(self, key_hash, key_builder):
# Only called for instances of this class, not for the class itself
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