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Fix flip to handle negative axis correctly #1628

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Merged
merged 5 commits into from
Oct 4, 2025
+28 −6
Merged

Fix flip to handle negative axis correctly #1628

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ab0396b
Initial plan
Copilot Oct 4, 2025
553dba5
Fix pt.flip to handle negative axis correctly using normalize_axis_tuple
Copilot Oct 4, 2025
b2b5e96
Expand existing test_flip function to include negative axis tests
Copilot Oct 4, 2025
2fca051
Fix mypy error by using separate variable for normalized axis
Copilot Oct 4, 2025
a7a183a
Fix ruff formatting issues
Copilot Oct 4, 2025
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13 changes: 7 additions & 6 deletions pytensor/tensor/subtensor.py
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@
from pytensor.graph.utils import MethodNotDefined
from pytensor.link.c.op import COp
from pytensor.link.c.params_type import ParamsType
from pytensor.npy_2_compat import numpy_version, using_numpy_2
from pytensor.npy_2_compat import normalize_axis_tuple, numpy_version, using_numpy_2
from pytensor.printing import Printer, pprint, set_precedence
from pytensor.scalar.basic import ScalarConstant, ScalarVariable
from pytensor.tensor import (
Expand Down Expand Up @@ -3369,11 +3369,12 @@ def flip(
if axis is None:
index = ((slice(None, None, -1)),) * arr.ndim
else:
if isinstance(axis, int):
axis = (axis,)
normalized_axis = normalize_axis_tuple(axis, arr.ndim)
index = tuple(
[
slice(None, None, -1) if i in axis else slice(None, None, None)
slice(None, None, -1)
if i in normalized_axis
else slice(None, None, None)
for i in range(arr.ndim)
]
)
Expand All @@ -3382,9 +3383,9 @@ def flip(


__all__ = [
"take",
"flip",
"slice_at_axis",
"inc_subtensor",
"set_subtensor",
"slice_at_axis",
"take",
]
21 changes: 21 additions & 0 deletions tests/tensor/test_subtensor.py
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Expand Up @@ -3147,6 +3147,27 @@ def test_flip(size: tuple[int]):
f = pytensor.function([x_pt], z, mode="FAST_COMPILE")
np.testing.assert_allclose(expected, f(x), atol=ATOL, rtol=RTOL)

# Test single negative axis
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This whole test is so overkill but predates the PR

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@jessegrabowski jessegrabowski Oct 4, 2025 •
edited
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I'm sure whoever wrote it was a really smart handsome guy who believed in making sure our code works great in every possible case

for axis in range(-x.ndim, 0):
expected = np.flip(x, axis=axis)
z = flip(x_pt, axis=axis)
f = pytensor.function([x_pt], z, mode="FAST_COMPILE")
np.testing.assert_allclose(expected, f(x), atol=ATOL, rtol=RTOL)

# Test tuple with negative axes
if x.ndim > 1:
expected = np.flip(x, axis=(-1, -2))
z = flip(x_pt, axis=(-1, -2))
f = pytensor.function([x_pt], z, mode="FAST_COMPILE")
np.testing.assert_allclose(expected, f(x), atol=ATOL, rtol=RTOL)

# Test mixed positive and negative axes
if x.ndim >= 2:
expected = np.flip(x, axis=(0, -1))
z = flip(x_pt, axis=(0, -1))
f = pytensor.function([x_pt], z, mode="FAST_COMPILE")
np.testing.assert_allclose(expected, f(x), atol=ATOL, rtol=RTOL)


class TestBenchmarks:
@pytest.mark.parametrize(
Expand Down
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