Fix map_blocks examples

[TomAugspurger]

The examples on master raised with

ValueError: Result from applying user function has unexpected coordinate variables {'month'}.

This PR updates the example to include the month coordinate. pytest --doctest-modules passes on these three now.

[TomAugspurger]

Hopefully this is the best way to include this coordinate. Just doing DataArray(..., dims=["time"], coords={"time": time, "month": time.month}) raised with

ValueError: coordinate month has dimensions ('month',), but these are not a subset of the DataArray dimensions ['time']

[max-sixty]

Thanks @TomAugspurger , appreciate the fix.

This is part of the broader #3837

[TomAugspurger]

The doc failure looks unrelated:

>>>-------------------------------------------------------------------------
Exception in /home/docs/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/doc/plotting.rst at block ending on line None
Specify :okexcept: as an option in the ipython:: block to suppress this message
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-75-c7d6afd7f8c5> in <module>
----> 1 g_simple = t.plot(x="lon", y="lat", col="time", col_wrap=3)

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/plot/plot.py in __call__(self, **kwargs)
    444 
    445     def __call__(self, **kwargs):
--> 446         return plot(self._da, **kwargs)
    447 
    448     # we can't use functools.wraps here since that also modifies the name / qualname

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/plot/plot.py in plot(darray, row, col, col_wrap, ax, hue, rtol, subplot_kws, **kwargs)
    198     kwargs["ax"] = ax
    199 
--> 200     return plotfunc(darray, **kwargs)
    201 
    202 

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/plot/plot.py in newplotfunc(darray, x, y, figsize, size, aspect, ax, row, col, col_wrap, xincrease, yincrease, add_colorbar, add_labels, vmin, vmax, cmap, center, robust, extend, levels, infer_intervals, colors, subplot_kws, cbar_ax, cbar_kwargs, xscale, yscale, xticks, yticks, xlim, ylim, norm, **kwargs)
    636             # Need the decorated plotting function
    637             allargs["plotfunc"] = globals()[plotfunc.__name__]
--> 638             return _easy_facetgrid(darray, kind="dataarray", **allargs)
    639 
    640         plt = import_matplotlib_pyplot()

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/plot/facetgrid.py in _easy_facetgrid(data, plotfunc, kind, x, y, row, col, col_wrap, sharex, sharey, aspect, size, subplot_kws, ax, figsize, **kwargs)
    642 
    643     if kind == "dataarray":
--> 644         return g.map_dataarray(plotfunc, x, y, **kwargs)
    645 
    646     if kind == "dataset":

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/plot/facetgrid.py in map_dataarray(self, func, x, y, **kwargs)
    263         # Get x, y labels for the first subplot
    264         x, y = _infer_xy_labels(
--> 265             darray=self.data.loc[self.name_dicts.flat[0]],
    266             x=x,
    267             y=y,

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/core/dataarray.py in __getitem__(self, key)
    196             labels = indexing.expanded_indexer(key, self.data_array.ndim)
    197             key = dict(zip(self.data_array.dims, labels))
--> 198         return self.data_array.sel(**key)
    199 
    200     def __setitem__(self, key, value) -> None:

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/core/dataarray.py in sel(self, indexers, method, tolerance, drop, **indexers_kwargs)
   1147 
   1148         """
-> 1149         ds = self._to_temp_dataset().sel(
   1150             indexers=indexers,
   1151             drop=drop,

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/core/dataset.py in sel(self, indexers, method, tolerance, drop, **indexers_kwargs)
   2099         """
   2100         indexers = either_dict_or_kwargs(indexers, indexers_kwargs, "sel")
-> 2101         pos_indexers, new_indexes = remap_label_indexers(
   2102             self, indexers=indexers, method=method, tolerance=tolerance
   2103         )

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/core/coordinates.py in remap_label_indexers(obj, indexers, method, tolerance, **indexers_kwargs)
    394     }
    395 
--> 396     pos_indexers, new_indexes = indexing.remap_label_indexers(
    397         obj, v_indexers, method=method, tolerance=tolerance
    398     )

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/core/indexing.py in remap_label_indexers(data_obj, indexers, method, tolerance)
    268             coords_dtype = data_obj.coords[dim].dtype
    269             label = maybe_cast_to_coords_dtype(label, coords_dtype)
--> 270             idxr, new_idx = convert_label_indexer(index, label, dim, method, tolerance)
    271             pos_indexers[dim] = idxr
    272             if new_idx is not None:

~/checkouts/readthedocs.org/user_builds/xray/checkouts/4305/xarray/core/indexing.py in convert_label_indexer(index, label, index_name, method, tolerance)
    187                 indexer = index.get_loc(label.item())
    188             else:
--> 189                 indexer = index.get_loc(
    190                     label.item(), method=method, tolerance=tolerance
    191                 )

~/checkouts/readthedocs.org/user_builds/xray/conda/4305/lib/python3.8/site-packages/pandas/core/indexes/datetimes.py in get_loc(self, key, method, tolerance)
    620         else:
    621             # unrecognized type
--> 622             raise KeyError(key)
    623 
    624         try:

KeyError: 1356998400000000000
<<<-------------------------------------------------------------------------

[max-sixty]

That does look unrelated. Thanks @TomAugspurger

[max-sixty]

Separately, I'm crunched at the moment but if anyone has any cycles to look at that failure that would be great. Doc build has not been kind to us recently...

[keewis]

the failure is #4283 and should be fixed by #4292. Also, there are warnings about *args, **kwargs, which will be fixed by the upcoming sphinx release (scheduled to be released in about 4 days). If we don't want to wait for that, I guess we can disable fail_on_warnings again?