Fix bBitMinHash NumPy pickling issue#248
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ekzhu merged 2 commits intoekzhu:masterfrom Nov 3, 2025
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Update: edited Ubuntu repo in tests as in #246. The main reason I submitted a separate PR for this change is because this PR as a doc might be useful for posterity, since this is kind of a non-trivial change. |
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cc @ekzhu |
ekzhu
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Nov 3, 2025
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cc @ekzhu
Problem:
Recent PRs such as #246 failed tests in Python 3.11 due to inconsistencies in the way that NumPy handled type coercion in certain functions (such as left_shift
<<). This led to an issue where, in more recent versions of Python, when pickling hashvalues in bBitMinHash the hashvalues would overflow to zero (because NumPy, being strict, refused to coerce the type from np.uint32 to np.uint64), effectively removing the ability to pickle these objects - and worse, failing silently.This problem was not present in previous NumPy versions (e.g., 1.x) because they were more lenient with type coercion and would implicitly change the hashvalue type to np.uint64.
Solution:
We resolve this issue by instead performing the bitwise operations in bBitMinHash's
__getstate__routine in native Python BigInteger type. This type has theoretically unlimited precision which avoids overflows. Moreover, it is implicitly coerced to np.uint64 as we expect. This works across NumPy versions and therefore across Python versions as well.References
NEP 50 - Promotion rules for Python scalars
[DOC] Changes to NumPy data type promotion