Assigning a NaN to Quantity does not work

[hgrecco]

Assigning a NaN to Quantity does not work:

>>> import pint
>>> ureg = pint.UnitRegistry()
>>> q = [1, 2, 3, 4] * ureg.meter
>>> q[0] = np.nan
Traceback (most recent call last):
...
ValueError
>>> q[0] = float('NaN')
Traceback (most recent call last):
...
ValueError

See #126

[mankoff]

The behavior here is the same as the python-quantities package, and does work in my opinion.

q[0] = np.nan * ureg.meter

is more cumbersome, but is also logical (to me).

[hgrecco]

It is logical, but given that NaN is Not a Number, i would be fine if this works:

q[0] = np.nan

[mankoff]

Agreed that should work. But the edge case of Inf should not work like that, since infinity does have units.

[hgrecco]

agreed

[s-celles]

It should be

q = [1.0, 2, 3, 4] * ureg.meter
q[0] = np.nan

because

In [32]: q = [1, 2, 3, 4] * ureg.meter
    ...: q[0] = np.nan
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-32-b94d2d97deac> in <module>
      1 q = [1, 2, 3, 4] * ureg.meter
----> 2 q[0] = np.nan

~/anaconda3/lib/python3.7/site-packages/pint/quantity.py in __setitem__(self, key, value)
   1407         try:
   1408             if math.isnan(value):
-> 1409                 self._magnitude[key] = value
   1410                 return
   1411         except (TypeError, DimensionalityError):

ValueError: cannot convert float NaN to integer