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Fix subtraction of TimeDuration of, and from, Data#288

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sadielbartholomew merged 3 commits intoNCAS-CMS:masterfrom
sadielbartholomew:fix-timeduration-sub-i287
Dec 21, 2021
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Fix subtraction of TimeDuration of, and from, Data#288
sadielbartholomew merged 3 commits intoNCAS-CMS:masterfrom
sadielbartholomew:fix-timeduration-sub-i287

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@sadielbartholomew sadielbartholomew commented Dec 20, 2021

Close #287 and add a test to capture it that bug, as well as a similar bug with a different traceback emering if the inverse is tried i..e the data subtracted from the timeduration (which I guess makes sense and should work, though isn't a very natural operation), namely (this report results from adding the new test lines to the master branch:

test_TimeDuration (__main__.TimeDurationTest) ... ok
test_TimeDuration_arithmetic (__main__.TimeDurationTest) ... ERROR
test_TimeDuration_bounds (__main__.TimeDurationTest) ... ok
test_TimeDuration_interval (__main__.TimeDurationTest) ... ok
test_TimeDuration_iso (__main__.TimeDurationTest) ... ok
test_Timeduration__days_in_month (__main__.TimeDurationTest) ... ok

======================================================================
ERROR: test_TimeDuration_arithmetic (__main__.TimeDurationTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_TimeDuration.py", line 487, in test_TimeDuration_arithmetic
    t2 = dt - da
  File "/home/sadie/cf-python/cf/timeduration.py", line 550, in __sub__
    return self._data_arithmetic(other, "__sub__")
  File "/home/sadie/cf-python/cf/timeduration.py", line 894, in _data_arithmetic
    return Data(dt, units=other.Units)
  File "/home/sadie/cf-python/cf/data/data.py", line 665, in __init__
    map(str, (x.year, x.month, x.day))
AttributeError: 'NotImplementedType' object has no attribute 'year'

----------------------------------------------------------------------

where commenting our the t2 = dt - da line and anything referring to t2 reveals the error Dan reported (for the full traceback it is:)

test_TimeDuration (__main__.TimeDurationTest) ... ok
test_TimeDuration_arithmetic (__main__.TimeDurationTest) ... ERROR
test_TimeDuration_bounds (__main__.TimeDurationTest) ... ok
test_TimeDuration_interval (__main__.TimeDurationTest) ... ok
test_TimeDuration_iso (__main__.TimeDurationTest) ... ok
test_Timeduration__days_in_month (__main__.TimeDurationTest) ... ok

======================================================================
ERROR: test_TimeDuration_arithmetic (__main__.TimeDurationTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_TimeDuration.py", line 488, in test_TimeDuration_arithmetic
    t3 = da - dt
TypeError: unsupported operand type(s) for -: 'Data' and 'TimeDuration'

----------------------------------------------------------------------

Fix suggestion

@davidhassell my suggestion is to change the implementation of __rsub__ to that shown, especially given the equivalently simple implementations of __radd__ and __rmul__, though because those are commutative and sub isn't, I would like to check that the idea is OK - perhaps relating to the non-commutativity __rsub__ must be done differently? If so, happy to change the approach, but something about the current implementation certainly isn't working and needs to be fixed and/or changed, and my suggestion does work at least...

@sadielbartholomew sadielbartholomew added the bug Something isn't working label Dec 20, 2021
@sadielbartholomew sadielbartholomew self-assigned this Dec 20, 2021
@sadielbartholomew sadielbartholomew changed the title Fix timeduration sub i287 Fix subtraction of TimeDuration of, and from, Data Dec 20, 2021
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davidhassell commented Dec 20, 2021 •
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Thanks, Sadie - I'll have a look tomorrow.

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sadielbartholomew commented Dec 21, 2021

CI test failures are both due to a lack of test_file.nc, so unrelated. I have noticed that this file is missing often locally too (I have in the test directory a copy I created to easily re-create it for these occasions 🙂 ). Is that file meant to be generated by the test set-up, David? If not it has gone AWOL so we should commit it back to the test directory.

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davidhassell approved these changes Dec 21, 2021
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Hi Sadie, looks good, thanks.

@sadielbartholomew sadielbartholomew merged commit 4fe10f3 into NCAS-CMS:master Dec 21, 2021
@davidhassell davidhassell added this to the 3.12.0 milestone Jan 4, 2022
@sadielbartholomew sadielbartholomew mentioned this pull request Jan 7, 2022
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subtraction of cf.TimeDuration fails

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