issue_comments

No problem ! Thanks everyone for helping me get up to speed :)

@keewis thanks for this! I've added what I think is a suitable test for DataArrays, do you think it's also a good idea to have a DataSet test?

This could test that dataarray.chunk("auto").data is the same as dataarray.data.rechunk("auto") (or something like that).

@dcherian Thanks for the tip:) Quick question: Is there a reason why you're specifying the .data here? Also I think I'm missing something because I don't get what the difference between .chunk() and .rechunk() would be in this case.

Cheers! I forgot about the tests, will add them this week or next hopefully

@dcherian do you have any idea about this mypy Type error? I can't find much (accessible) documentation on how the Union[] is working in this context.

xarray/core/dataset.py:1737: error: Argument 2 to "fromkeys" of "dict" has incompatible type "Union[Number, Mapping[Hashable, Union[None, Number, Tuple[Number, ...]]]]"; expected "Union[None, Number, Tuple[Number, ...]]" xarray/core/dataset.py:1740: error: Item "Number" of "Union[Number, Mapping[Hashable, Union[None, Number, Tuple[Number, ...]]]]" has no attribute "keys"

Edit: thanks to everyone for your help so far!

Okay so I've traced the error back to the map_blocks() function. I don't fully understand the code for this function in xarray/core/parallel.py, but here's a quick report on the different behaviours.

Normally, when using the make_ds() and make_da() functions in test_dask.py, without any changes to ds.chunk() we have:

```python

def func(obj): ... result = obj + obj.x + 5 * obj.y ... return result ... xr.map_blocks(func, ds).unify_chunks().chunks Frozen(SortedKeysDict({'x': (4, 4, 2), 'y': (5, 5, 5, 5), 'z': (4,)})) func(ds).chunk().unify_chunks().chunks Frozen(SortedKeysDict({'x': (4, 4, 2), 'y': (5, 5, 5, 5), 'z': (4,)})) ```

However, when I use the changes I've made to dataset.py (changing isinstance(chunks, Number) to is_scalar(chunks)), the behaviour becomes:

```python

xr.map_blocks(func, ds).unify_chunks().chunks Frozen(SortedKeysDict({'x': (4, 4, 2), 'y': (5, 5, 5, 5), 'z': (4,)})) func(ds).chunk().unify_chunks().chunks Frozen(SortedKeysDict({'x': (10,), 'y': (20,), 'z': (4,)})) ```

Which means that it now fails the test_map_blocks() call in test_dask.py line 1077.

I've tried to follow through the code and see what is actually happening when this change is made, but I'm out of my depth here. My guess is that is_scalar(chunks) is giving the wrong behaviour when chunks=None ?

Edit: I think that's the problem!
```python

isinstance(None, numbers.Number) False is_scalar(None) True ```

I'll add in something to catch Nones and see if it fixes the error...

No unpushed commits

Do you mean the master merge? If that's wrong would you be able to fix it for me? My bad, hopefully i'll be able to do it more cleanly in future

Okay, that makes sense. Though, it seems that I forked the master branch before @kmuehlbauer's commit, which fixed this flake8 issue? So I think I need to make a new fork?

Okay cheers both! I'll have a look at these now.

@keewis sorry I'm still getting used to using this side of Git at the moment, could you clarify what you mean by merge master ? Do you mean merge with my local master?

In my git clone, when I run the flake8 and black . tests, I get the following messages.

(xarray-tests) Andrews-MacBook-Pro-2:xarray andrewwilliams$ black . All done! ✨ 🍰 ✨ 143 files left unchanged. (xarray-tests) Andrews-MacBook-Pro-2:xarray andrewwilliams$ flake8 ./xarray/backends/memory.py:43:32: E741 ambiguous variable name 'l' ./xarray/backends/common.py:244:32: E741 ambiguous variable name 'l' ./xarray/backends/.ipynb_checkpoints/memory-checkpoint.py:43:32: E741 ambiguous variable name 'l'

I'm not sure why something has changed in these files (I haven't touched them), I also can't work out what the l variable is meant to be doing there.

Could this somehow be associated with loads of the checks failing below? Thanks! :)