regression in error message for DatetimeIndex subtraction

[simonjayhawkins]

Code Sample, a copy-pastable example if possible

import pandas as pd
td = pd.Timedelta('1 days')
dti = pd.date_range('20130101', periods=3, name='bar')
td - dti

Problem description

0.25.0.dev0+179.g0a61ecdf6

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\simon\OneDrive\code\pandas-simonjayhawkins\pandas\core\indexes\datetimelike.py", line 507, in __rsub__
    result = self._data.__rsub__(maybe_unwrap_index(other))
  File "C:\Users\simon\OneDrive\code\pandas-simonjayhawkins\pandas\core\arrays\datetimelike.py", line 1325, in __rsub__
    return -(self - other)
TypeError: bad operand type for unary -: 'DatetimeArray'

Expected Output

same as 0.23.4

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-2a4f19a48f3e> in <module>
      3 td = pd.Timedelta('1 days')
      4 dti = pd.date_range('20130101', periods=3, name='bar')
----> 5 td - dti

~\Anaconda3\lib\site-packages\pandas\core\indexes\datetimelike.py in __rsub__(self, other)
    949                 from pandas import DatetimeIndex
    950                 return DatetimeIndex(other) - self
--> 951             return -(self - other)
    952         cls.__rsub__ = __rsub__
    953 

~\Anaconda3\lib\site-packages\pandas\core\ops.py in invalid_op(self, other)
    174     def invalid_op(self, other=None):
    175         raise TypeError("cannot perform {name} with this index type: "
--> 176                         "{typ}".format(name=name, typ=type(self).__name__))
    177 
    178     invalid_op.__name__ = name

TypeError: cannot perform __neg__ with this index type: DatetimeIndex

Output of pd.show_versions()

INSTALLED VERSIONS

commit: 0a61ecd
python: 3.7.2.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 158 Stepping 9, GenuineIntel
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: None.None

pandas: 0.25.0.dev0+179.g0a61ecdf6
pytest: 4.2.0
pip: 19.0.1
setuptools: 40.8.0
Cython: 0.29.5
numpy: 1.15.4
scipy: 1.2.1
pyarrow: 0.11.1
xarray: 0.11.3
IPython: 7.2.0
sphinx: 1.8.4
patsy: 0.5.1
dateutil: 2.7.5
pytz: 2018.9
blosc: None
bottleneck: 1.2.1
tables: 3.4.4
numexpr: 2.6.9
feather: None
matplotlib: 3.0.2
openpyxl: 2.6.0
xlrd: 1.2.0
xlwt: 1.3.0
xlsxwriter: 1.1.2
lxml.etree: 4.3.1
bs4: 4.7.1
html5lib: 1.0.1
sqlalchemy: 1.2.18
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: 0.2.0
fastparquet: 0.2.1
pandas_gbq: None
pandas_datareader: None
gcsfs: None

[jorisvandenbossche]

I am not sure it is a "regression" (I find the old one as confusing), but for sure it is not the most helpful error message.

For the DatetimeArray -> DatetimeIndex name in the error message, @TomAugspurger would that be something to use the rewrite_exception you added at some point somewhere?

[TomAugspurger]

I think if we're going py3 only we may be able to do the

result = self._data.__rsub__(maybe_unwrap_index(other))

as

try:
    result = self._data.__rsub__(maybe_unwrap_index(other))
except TypeError as e:
    raise TypeError("Cannot perfom ...") from e

[jbrockmendel]

i dont think this is worth worrying about, advocate closing

[simonjayhawkins]

sure