8000 BUG (I guess?): Make a @= b error out by njsmith · Pull Request #6000 · numpy/numpy · GitHub
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BUG (I guess?): Make a @= b error out #6000

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Merged
merged 1 commit into from
Jun 28, 2015
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BUG (I guess?): Make a @= b error out #6000

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BUG: Make a @= b error out 
Before this change, we defined a nb_matrix_multiply slot but not a
nb_inplace_matrix_multiply slot, which means that a statement like

  a @= b

would be silently expanded by the CPython interpreter to become

  a = a @ b

This is undesireable, because it produces unexpected memory
allocations, breaks view relationships, and so forth.

This commit adds a nb_inplace_matrix_multiply slot which simply errors
out, and suggests that users write 'a = a @ b' explicitly if that's
what they want.
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@njsmith
njsmith committed Jun 28, 2015
commit 1adcdf7aa5b20a9afd778290105ec327b705c93e
11 changes: 10 additions & 1 deletion numpy/core/src/multiarray/number.c
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Original file line number Diff line number Diff line change
Expand Up @@ -405,6 +405,15 @@ array_matrix_multiply(PyArrayObject *m1, PyObject *m2)
0, nb_matrix_multiply);
return PyArray_GenericBinaryFunction(m1, m2, matmul);
}

static PyObject *
array_inplace_matrix_multiply(PyArrayObject *m1, PyObject *m2)
{
PyErr_SetString(PyExc_TypeError,
"In-place matrix multiplication is not (yet) supported. "
"Use 'a = a @ b' instead of 'a @= b'.");
return NULL;
}
#endif

/* Determine if object is a scalar and if so, convert the object
Expand Down Expand Up @@ -1092,6 +1101,6 @@ NPY_NO_EXPORT PyNumberMethods array_as_number = {
(unaryfunc)array_index, /*nb_index */
#if PY_VERSION_HEX >= 0x03050000
(binaryfunc)array_matrix_multiply, /*nb_matrix_multiply*/
(binaryfunc)NULL, /*nb_inplacematrix_multiply*/
(binaryfunc)array_inplace_matrix_multiply, /*nb_inplace_matrix_multiply*/
#endif
};
13 changes: 13 additions & 0 deletions numpy/core/tests/test_multiarray.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4322,6 +4322,19 @@ def __rmatmul__(self, other):
assert_equal(self.matmul(a, b), "A")
assert_equal(self.matmul(b, a), "A")

def test_matmul_inplace():
# It would be nice to support in-place matmul eventually, but for now
# we don't have a working implementation, so better just to error out
# and nudge people to writing "a = a @ b".
a = np.eye(3)
b = np.eye(3)
assert_raises(TypeError, a.__imatmul__, b)
import operator
assert_raises(TypeError, operator.imatmul, a, b)
# we avoid writing the token `exec` so as not to crash python 2's
# parser
exec_ = getattr(builtins, "exec")
assert_raises(TypeError, exec_, "a @= b", globals(), locals())

class TestInner(TestCase):

Expand Down
0