Fix compatibility of Tuple's hash function #3460

TeamTamoad · 2021-11-27T08:05:50Z

Change hash function implementation of Tuple to compatible with CPython's implementation.

Summary by CodeRabbit

Bug Fixes
- Updated tuple hashing to use a new algorithm that produces platform-specific hash values, improving consistency with expected hash outputs.
- Adjusted tests so that tuple hash tests are now required to pass, reflecting the improved hashing implementation.

youknowone

The change looks great, but by looking at the CI result, range() hash must follow the reuslt of tuple. Could you also update range.__hash__ in the same way?

You can extract hash function like fn tuple_hash(elements: &[PyObjectRef], vm: &VirtualMachine) and call it form PyTuple::hash like tuple_hash(zelf.as_slice())

youknowone · 2021-11-27T14:23:30Z

The new bug is bug of exec. Somehow when __hash__ is added by exec, it doesn't run update_slot.
As the result, the upper test passes but the lower test fails

import dataclasses

@dataclasses.dataclass(unsafe_hash=True)
class X:
    pass


a = X().__hash__()
b = ().__hash__()
assert a == b, '{} {}'.format(a, b)

a = hash(X())
b = hash(())
assert a == b, '{} {}'.format(a, b)

youknowone · 2021-11-27T14:24:05Z

@coolreader18 do you have any idea?

coderabbitai · 2025-06-27T04:54:20Z

Walkthrough

The updates remove the @unittest.expectedFailure decorator from a tuple hash test in the Python test suite and replace the tuple hash function in the Rust backend with a new, custom implementation. The new hash function uses platform-dependent constants and a custom mixing algorithm for tuple elements.

Changes

File(s)	Change Summary
Lib/test/test_tuple.py	Removed `@unittest.expectedFailure` decorator and comment from `test_hash_exact` in `TupleTest`.
vm/src/builtins/tuple.rs	Replaced tuple hash function with a custom implementation using platform-dependent constants.
vm/src/builtins/tuple.rs (import)	Expanded import to include `PyUHash` from the `hash` module.

Poem

In tupleland, a hash anew,
With primes and spins, the numbers grew.
No longer failing, tests now pass,
As rabbits code with gentle sass.
From Python's lair to Rusty den,
We hash our tuples once again!
🐇✨

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Lib/test/test_tuple.py (0 hunks)
vm/src/builtins/tuple.rs (2 hunks)

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Lib/test/test_tuple.py

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🧠 Learnings (2)

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Learnt from: CR
PR: RustPython/RustPython#0
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Timestamp: 2025-06-26T12:52:11.109Z
Learning: When a test fails due to unsupported Python syntax or features, keep the test as '@unittest.expectedFailure' and document the reason, rather than modifying the test logic or data.

Learnt from: CR
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File: .github/copilot-instructions.md:0-0
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Learning: Minimize modifications to CPython standard library files in the Lib/ directory; bug fixes should be made through Rust code modifications whenever possible.

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vm/src/builtins/tuple.rs (3)

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File: .github/copilot-instructions.md:0-0
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Learning: Use the macro system (such as 'pyclass', 'pymodule', 'pyfunction') when implementing Python functionality in Rust for RustPython.

Learnt from: CR
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File: .github/copilot-instructions.md:0-0
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Learning: Follow Rust best practices for error handling and memory management in all RustPython Rust code.

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File: .github/copilot-instructions.md:0-0
Timestamp: 2025-06-26T12:52:11.109Z
Learning: When implementing a Python module in Rust for RustPython, use the #[pymodule] attribute and expose functions and classes using #[pyfunction], #[pyclass], and #[pymethod] as appropriate.

🔇 Additional comments (2)

vm/src/builtins/tuple.rs (2)

2-5: LGTM: Import change supports new hash implementation

The addition of PyUHash import is necessary for the new tuple hash function implementation.

594-629: Verify hash algorithm constants and implementation against CPython

The new tuple hash implementation uses platform-specific constants and a custom combining algorithm that should match CPython's behavior exactly. However, the PR comments indicate there may still be compatibility issues with dataclasses and exec-related scenarios.

Please verify that:

The constants (PRIME1, PRIME2, PRIME5, ROTATE) match CPython's tuple hash implementation exactly

The algorithm steps are identical to CPython's implementation

The magic constant 3527539 in the final addition is correct
#!/bin/bash
# Description: Search for CPython's tuple hash implementation for comparison
# Expected: Find references to similar constants and algorithm structure

# Search for tuple hash implementation patterns
rg -A 10 -B 5 "tuple.*hash|hash.*tuple" --type rust

# Look for any existing hash-related tests that might be affected
rg -A 5 -B 5 "test.*hash.*tuple|tuple.*test.*hash" --type rust
The exec-related issue mentioned in the PR comments suggests this implementation may not fully resolve the compatibility problem. Consider addressing the dataclass hash inconsistency described in the PR discussion.

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youknowone

Great, I have no idea which certain point made the changes, but it now works!

youknowone requested changes Nov 27, 2021

View reviewed changes

youknowone force-pushed the hash-tuple branch from dfb0104 to cc65be9 Compare August 4, 2022 20:21

youknowone force-pushed the hash-tuple branch from cc65be9 to c2955f8 Compare February 22, 2023 12:56

youknowone mentioned this pull request Feb 22, 2023

Prepare to implement hash for tuple #4548

Merged

youknowone force-pushed the hash-tuple branch from c2955f8 to 1d80da9 Compare February 22, 2023 13:09

youknowone mentioned this pull request Mar 6, 2023

Update to pass test for unhashable collections #4640

Merged

youknowone force-pushed the hash-tuple branch from 1d80da9 to 70dfd90 Compare March 10, 2023 17:46

youknowone force-pushed the hash-tuple branch from 70dfd90 to fd27a3d Compare April 8, 2025 05:31

Implement true hash for tuple

8b0f88e

youknowone force-pushed the hash-tuple branch from fd27a3d to 8b0f88e Compare June 27, 2025 04:54

youknowone approved these changes Jun 27, 2025

View reviewed changes

youknowone merged commit 2ea77b4 into RustPython:main Jun 27, 2025
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Fix compatibility of Tuple's hash function #3460

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