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BUG: slice_canonize incorrectly raising #37524

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Merged
merged 4 commits into from
Oct 31, 2020
Merged

BUG: slice_canonize incorrectly raising #37524

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b364642
BUG: slice_canonize incorrectly raising
jbrockmendel Oct 30, 2020
0ef3718
GH ref
jbrockmendel Oct 30, 2020
7d160cd
Merge branch 'master' of https://github.com/pandas-dev/pandas into bu…
jbrockmendel Oct 31, 2020
32c99b9
Merge branch 'master' of https://github.com/pandas-dev/pandas into bu…
jbrockmendel Oct 31, 2020
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4 changes: 2 additions & 2 deletions pandas/_libs/internals.pyx
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Original file line number Diff line number Diff line change
Expand Up @@ -207,7 +207,7 @@ cdef slice slice_canonize(slice s):
Convert slice to canonical bounded form.
"""
cdef:
Py_ssize_t start = 0, stop = 0, step = 1, length
Py_ssize_t start = 0, stop = 0, step = 1

if s.step is None:
step = 1
Expand Down Expand Up @@ -239,7 +239,7 @@ cdef slice slice_canonize(slice s):
if stop > start:
stop = start

if start < 0 or (stop < 0 and s.stop is not None):
if start < 0 or (stop < 0 and s.stop is not None and step > 0):
raise ValueError("unbounded slice")

if stop < 0:
Expand Down
7 changes: 7 additions & 0 deletions pandas/tests/internals/test_internals.py
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Expand Up @@ -922,6 +922,13 @@ def test_zero_step_raises(self, slc):
with pytest.raises(ValueError, match=msg):
BlockPlacement(slc)

def test_slice_canonize_negative_stop(self):
# GH#37524 negative stop is OK with negative step and positive start
slc = slice(3, -1, -2)

bp = BlockPlacement(slc)
assert bp.indexer == slice(3, None, -2)

@pytest.mark.parametrize(
"slc",
[
Expand Down