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Do not change coordinate inplace when throwing error #5957

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Nov 9, 2021
Merged

Do not change coordinate inplace when throwing error #5957

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5affeb7
Fix bug and add test
gcaria Nov 8, 2021
48c6ee2
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gcaria Nov 8, 2021
b354119
Edit only _inplace_binary_op
gcaria Nov 9, 2021
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4 changes: 4 additions & 0 deletions xarray/core/variable.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2418,6 +2418,10 @@ def _inplace_binary_op(self, other, f):
if dims != self.dims:
raise ValueError("dimensions cannot change for in-place operations")
with np.errstate(all="ignore"):
# Give a chance to Variable.values.setter to throw error if needed
# without updating self_data inplace
if isinstance(self_data, np.ndarray):
self.values = f(self_data.copy(), other_data)
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Defensively copying xarray.Variable data would negate the main purpose of in-place binary arithmetic, which is to avoid copies.

For fixing #5036, what about instead overriding _inplace_binary_op on the IndexVariable subclass? I think we could just make it raise a TypeError instead of attempting to do the computation.

self.values = f(self_data, other_data)
return self

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10 changes: 10 additions & 0 deletions xarray/tests/test_dataarray.py
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Expand Up @@ -1987,6 +1987,16 @@ def test_inplace_math_basics(self):
assert_array_equal(b.values, x)
assert source_ndarray(b.values) is x

def test_inplace_math_error(self):
data = np.random.rand(4)
times = np.arange(4)
foo = DataArray(data, coords=[times], dims=["time"])
b = times.copy()
with pytest.raises(ValueError, match=r"Cannot assign to the .values"):
foo.coords["time"] += 1
# Check error throwing prevented inplace operation
assert_array_equal(foo.coords["time"], b)

def test_inplace_math_automatic_alignment(self):
a = DataArray(range(5), [("x", range(5))])
b = DataArray(range(1, 6), [("x", range(1, 6))])
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