issue_comments: 280680476

Maybe related? Selection with slices also doesn't work:

python da = xr.DataArray(pd.Series(1, pd.period_range('1990-1', '2000-12', freq='M'))) da.sel(dim_0='1991-07') # works fine da.sel(dim_0='1992-02') # works fine da.sel(dim_0=slice('1991-07', '1992-02'))

Throws:

```

AssertionError Traceback (most recent call last) <ipython-input-35-2e962ee8a791> in <module>() 2 da.sel(dim_0='1991-07') # works fine 3 da.sel(dim_0='1992-02') # works fine ----> 4 da.sel(dim_0=slice('1991-07', '1992-02'))

/home/mowglie/.pyvirtualenvs/py3/lib/python3.5/site-packages/xarray/core/dataarray.py in sel(self, method, tolerance, drop, indexers) 668 """ 669 pos_indexers, new_indexes = indexing.remap_label_indexers( --> 670 self, indexers, method=method, tolerance=tolerance 671 ) 672 result = self.isel(drop=drop, pos_indexers)

/home/mowglie/.pyvirtualenvs/py3/lib/python3.5/site-packages/xarray/core/indexing.py in remap_label_indexers(data_obj, indexers, method, tolerance) 286 else: 287 idxr, new_idx = convert_label_indexer(index, label, --> 288 dim, method, tolerance) 289 pos_indexers[dim] = idxr 290 if new_idx is not None:

/home/mowglie/.pyvirtualenvs/py3/lib/python3.5/site-packages/xarray/core/indexing.py in convert_label_indexer(index, label, index_name, method, tolerance) 183 indexer = index.slice_indexer(_try_get_item(label.start), 184 _try_get_item(label.stop), --> 185 _try_get_item(label.step)) 186 if not isinstance(indexer, slice): 187 # unlike pandas, in xarray we never want to silently convert a slice

/home/mowglie/.pyvirtualenvs/py3/lib/python3.5/site-packages/pandas/indexes/base.py in slice_indexer(self, start, end, step, kind) 2995 """ 2996 start_slice, end_slice = self.slice_locs(start, end, step=step, -> 2997 kind=kind) 2998 2999 # return a slice

/home/mowglie/.pyvirtualenvs/py3/lib/python3.5/site-packages/pandas/indexes/base.py in slice_locs(self, start, end, step, kind) 3174 start_slice = None 3175 if start is not None: -> 3176 start_slice = self.get_slice_bound(start, 'left', kind) 3177 if start_slice is None: 3178 start_slice = 0

/home/mowglie/.pyvirtualenvs/py3/lib/python3.5/site-packages/pandas/indexes/base.py in get_slice_bound(self, label, side, kind) 3113 # For datetime indices label may be a string that has to be converted 3114 # to datetime boundary according to its resolution. -> 3115 label = self._maybe_cast_slice_bound(label, side, kind) 3116 3117 # we need to look up the label

/home/mowglie/.pyvirtualenvs/py3/lib/python3.5/site-packages/pandas/tseries/period.py in _maybe_cast_slice_bound(self, label, side, kind) 838 839 """ --> 840 assert kind in ['ix', 'loc', 'getitem'] 841 842 if isinstance(label, datetime):

AssertionError: ```