bool(Dataset(False)) is True

What happened:

v=True
bool(xr.DataArray(v)) # True
bool(xr.DataArray(v).to_dataset(name='var')) # True

v=False
bool(xr.DataArray(v)) # False
# unexpected behaviour below
bool(xr.DataArray(v).to_dataset(name='var')) # True

What you expected to happen:

bool(xr.DataArray(False).to_dataset(name='var')) # False

Maybe this is intentional and I dont understand why.

xr.version = ‘0.16.0’

[max-sixty]

We mirror numpy for DataArray and, per @keewis , Mapping for Dataset. I think we should have a fairly high bar for deviating from those.

For those who think bool(xr.Dataset(dict(x=False))) should evaluate to False, what do you think dict(x=False) should evaluate to?

IIUC, this is somewhat of an edge case — it’s only possible to coerce DataArray to bool when there’s exactly one element. (Not that we shouldn’t resolve)

This question seems to me to be conceptually similar to the question I described in #3315: “Should we treat a named DataArray and a single-variable Dataset as if they are the same?”

👍

[keewis]

If I remember correctly, Dataset inherits from dict and doesn’t define it’s own __bool__, so it has the behavior of dict.__bool__:

In [2]: bool(xr.Dataset())
Out[2]: False

In [3]: bool(xr.Dataset({"x": False}))
Out[3]: True

In [4]: bool({})
Out[4]: False

In [5]: bool({"x": False})
Out[5]: True