REF: use check_setitem_lengths in DTA.__setitem__

[jbrockmendel]

Turning this into a two-line check will make it easy to add to PandasArray.__setitem__ and Categorical.__setitem__, at which point we'll be able to move these methods up to NDArrayBackedExtensionArray.__setitem__

[jorisvandenbossche]

Looks good! Only a comment regarding the todo

[jorisvandenbossche]

I think yes?
But can you do that here, since the original code (I think?) did it.

[jbrockmendel]

the existing code does not check for length-match in the len==0 case. ill take a look at adding that check and getting rid of this comment

[jorisvandenbossche]

It actually is checked right now, because of the len(key) != len(value) before checking elif not len(key): (but it's clearly not tested ..)

As example:

In [1]: arr = pd.date_range("2012", periods=3)._data                                                                                                                                                               

In [2]: arr                                                                                                                                                                                                        
Out[2]: 
<DatetimeArray>
['2012-01-01 00:00:00', '2012-01-02 00:00:00', '2012-01-03 00:00:00']
Length: 3, dtype: datetime64[ns]

In [3]: arr[[]] = [pd.Timestamp("2012")]                                                                                                                                                                           
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-3-d4b75e105bf5> in <module>
----> 1 arr[[]] = [pd.Timestamp("2012")]

~/scipy/pandas/pandas/core/arrays/datetimelike.py in __setitem__(self, key, value)
    620                         f"'{len(value)}'."
    621                     )
--> 622                     raise ValueError(msg)
    623                 elif not len(key):
    624                     return

ValueError: shape mismatch: value array of length '0' does not match indexing result of length '1'.

[jbrockmendel]

Good catch; i was comparing against the existing check_setitem_lengths

[jreback]

use not len(value) (and same as above)

[jorisvandenbossche]

Personally I find if len(value) == 0: more readable / clearer about the intent ...

[jreback]

its not idiomatic python (though i tend to agree), either way as long as we are consistent, and unfortunately this is not consistent with the rest of the code base

[jorisvandenbossche]

@jbrockmendel can you add a test for the setitem case with zero-length indexer and non-zero length value (as it is clearly untested ..)

[jbrockmendel]

updated per suggestions

[jorisvandenbossche]

Thanks!