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Return NotImpelmented for arith ops with object-dtype Index subclasses #31109

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TomAugspurger opened this issue Jan 17, 2020 · 2 comments · Fixed by #31136
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Return NotImpelmented for arith ops with object-dtype Index subclasses #31109

TomAugspurger opened this issue Jan 17, 2020 · 2 comments · Fixed by #31136
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Blocker Blocking issue or pull request for an upcoming release Numeric Operations Arithmetic, Comparison, and Logical operations
Milestone
1.0.0

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@TomAugspurger
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This change in 1.0 impacted xarray

 In [22]: import xarray as xr

In [23]: import pandas as pd

In [24]: idx = pd.timedelta_range("1D", periods=5, freq="D")

In [25]: a = xr.cftime_range("2000", periods=5)

In [26]: idx + a
/Users/taugspurger/sandbox/pandas/pandas/core/arrays/datetimelike.py:1204: PerformanceWarning: Adding/subtracting array of DateOffsets to TimedeltaArray not vectorized
  PerformanceWarning,
Out[26]:
Index([2000-01-02 00:00:00, 2000-01-04 00:00:00, 2000-01-06 00:00:00,
       2000-01-08 00:00:00, 2000-01-10 00:00:00],
      dtype='object')

In [27]: a + idx
Out[27]:
CFTimeIndex([2000-01-02 00:00:00, 2000-01-04 00:00:00, 2000-01-06 00:00:00,
             2000-01-08 00:00:00, 2000-01-10 00:00:00],
            dtype='object')

cc @jbrockmendel @dcherian. Brock suggested checking type(other), and returning NotImplemented for index subclasses we don't know about, to give the subclass a chance to take over the op.
@TomAugspurger TomAugspurger added this to the 1.0.0 milestone Jan 17, 2020
@TomAugspurger TomAugspurger added Blocker Blocking issue or pull request for an upcoming release Numeric Operations Arithmetic, Comparison, and Logical operations labels Jan 17, 2020
@TomAugspurger TomAugspurger mentioned this issue Jan 17, 2020
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@jbrockmendel
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Should we try to get a short-term fix in for 1.0?

@TomAugspurger
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Yep, I think so.

TomAugspurger added a commit to TomAugspurger/pandas that referenced this issue Jan 19, 2020
@TomAugspurger
COMPAT: Return NotImplemented for subclassing
1a03084 
This changes index ops to check the *type* of the argument in index
ops, rather than just the dtype. This lets index subclasses take control
of binary ops when they know better what the result should be.

Closes pandas-dev#31109
This was referenced Jan 19, 2020
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TomAugspurger added a commit that referenced this issue Jan 28, 2020
@TomAugspurger
COMPAT: Return NotImplemented for subclassing (#31136)
3dc59d4 
* COMPAT: Return NotImplemented for subclassing

This changes index ops to check the *type* of the argument in index
ops, rather than just the dtype. This lets index subclasses take control
of binary ops when they know better what the result should be.

Closes #31109
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Blocker Blocking issue or pull request for an upcoming release Numeric Operations Arithmetic, Comparison, and Logical operations
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COMPAT: Return NotImplemented for subclassing TomAugspurger/pandas
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