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GeezerVison is showing github.com — Reject building a user monoid from a built-in BinaryOp by eriknw · Pull Request #617 · python-graphblas/python-graphblas

Reject building a user monoid from a built-in BinaryOp #617

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Merged
eriknw merged 1 commit into main from 36-monoid-builtin-binaryop-guard
Nov 11, 2026

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Reject building a user monoid from a built-in BinaryOp #617

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Reject building a user monoid from a built-in BinaryOp
eriknw Aug 5, 2026
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28 changes: 28 additions & 0 deletions 28 graphblas/core/operator/monoid.py
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,16 @@
_BUILTIN_UDT_MONOIDS = {"plus", "times", "min", "max"}


def _is_builtin_binaryop(binaryop):
"""True if ``binaryop`` wraps built-in GraphBLAS operators rather than a UDF.

Built-ins are the only binary ops constructed with neither a Python func nor
a numba func. That covers ``binary.numpy.float_power`` too, which is
assembled out of ``binary.pow``'s typed ops.
"""
return binaryop.orig_func is None and binaryop._numba_func is None


def _scalar_identity(monoid_name, scalar_dtype):
"""Return the identity for a single numeric (or bool) numpy dtype, or ``None``.

Expand Down Expand Up @@ -262,6 +272,24 @@ class Monoid(OpBase):
def _build(cls, name, binaryop, identity, *, is_idempotent=False, anonymous=False):
if type(binaryop) is not BinaryOp:
raise TypeError(f"binaryop must be a BinaryOp, not {type(binaryop)}")
if _is_builtin_binaryop(binaryop):
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@eriknw eriknw Nov 11, 2026

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I wonder whether it's actually worth making _is_builtin_binaryop a single-line helper functions that is used in one location.

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# Rejected up front, before any object is created: a built-in binaryop
# cannot back a user monoid. Its typed ops are ``TypedBuiltinBinaryOp``
# with no ``_monoid`` slot, so ``TypedUserMonoid`` would raise an opaque
# AttributeError partway through, having already repointed
# ``binary.<name>._monoid`` at the half-built monoid. Even if that were
# patched over, SuiteSparse ignores the identity handed to
# ``GrB_Monoid_new`` whenever the built-in op already has a built-in
# monoid (max, min, plus, times, any), so the result would silently
# disagree with ``monoid[dtype].identity``.
raise TypeError(
"binaryop must be a user-defined BinaryOp, not the built-in "
f"binary.{binaryop.name}. Built-in binary operators already own their "
"monoid association (binary.plus resolves to monoid.plus, and so on). "
"To build a monoid with a different identity, register the function as "
"a new BinaryOp (BinaryOp.register_new or BinaryOp.register_anonymous) "
"and pass that."
)
if name is None:
name = binaryop.name
new_type_obj = cls(
Expand Down
18 changes: 18 additions & 0 deletions 18 graphblas/tests/test_op.py
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Expand Up @@ -422,6 +422,24 @@ def bad_identity(x=0):
assert monoid.is_idempotent


def test_monoid_rejects_builtin_binaryop():
"""A built-in binaryop cannot back a user monoid.

Built-ins already own their monoid association (binary.max resolves to
monoid.max), and SuiteSparse silently ignores the identity passed to
GrB_Monoid_new for them, so accepting one would produce a monoid whose
Python-side identity disagrees with what GraphBLAS computes with.
"""
with pytest.raises(TypeError, match="must be a user-defined BinaryOp"):
Monoid.register_new("_bad_builtin_monoid", binary.max, 0)
with pytest.raises(TypeError, match="must be a user-defined BinaryOp"):
Monoid.register_anonymous(binary.plus, 1)
# The rejection happens before any object is created, so the built-in's
# own monoid association is untouched.
assert binary.max.monoid is monoid.max
assert not hasattr(gb.monoid, "_bad_builtin_monoid")


@pytest.mark.skipif("not supports_udfs")
@pytest.mark.slow
def test_semiring_parameterized():
Expand Down
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