BUG: Make bool(void_scalar) and void_scalar.astype(bool) consistent - #9856

I get slightly different results with Python 2.7 and 1.14-dev

In [13]: void(3).astype(bool)
Out[13]: True

In [14]: void(2).astype(bool)
Out[14]: True

In [15]: void(1).astype(bool)
Out[15]: True

In [16]: void(0).astype(bool)
Out[16]: False

...

In [23]: void('123').astype(bool)
Out[23]: True

In [24]: void('12').astype(bool)
Out[24]: True

In [25]: void('1').astype(bool)
Out[25]: True

In [26]: void('').astype(bool)
Out[26]: False

So always True unless empty, no warnings.

EDIT: Same with void array scalars.

Also differs for Python 3.

So the rule in all these cases will be that 0D arrays and scalars containing empty byte strings, empty unicode strings, and V scalars converted to boolean yield False, and all other cases yield True. I assume this extends consistently to higher dimensional arrays.

Turns out I mispoke about python 2, and hadn't tested void(0).

Also differs for Python 3.

Can you elaborate on this?

So the rule in all these cases will be that 0D arrays and scalars containing empty byte strings, empty unicode strings, and V scalars converted to boolean yield False,

Yes. This was already true when converting with bool(...). The rule for void is "all bytes are zero" → False.

There's nothing special about 0d here, other than the fact that the LHS of the test bool(x) == x.astype(bool) is meaningful

Actually, the above is what the previous patch did. This patch only affects the visible behaviour of void scalars, and leaves strings alone

This seems correct to me, but will need a release note.

Can you elaborate on this?

I get ValueError: setting an array element with a sequence., but may be doing something different.

This patch only affects the visible behaviour of void scalars

Yep, but there are tests waiting to be enabled for the others.

I get ValueError: setting an array element with a sequence.

You're right, I had a different execution path in my head. I've updated the top comment with correct information.

Release note added

Thanks Eric.