Allow assigning Not a Number to a quantity array.

Close #127

2 files changed, 16 insertions, 0 deletions

diff --git a/pint/quantity.py b/pint/quantity.py
index 2170962..d1834e2 100644
--- a/pint/quantity.py
+++ b/pint/quantity.py
@@ -10,6 +10,7 @@
 from __future__ import division, unicode_literals, print_function, absolute_import
 
 import copy
+import math
 import operator
 import functools
 
@@ -761,6 +762,10 @@ class _Quantity(object):
 
     def __setitem__(self, key, value):
         try:
+            if math.isnan(value):
+                self._magnitude[key] = value
+                return
+
             if isinstance(value, self.__class__):
                 factor = self.__class__(value.magnitude, value.units / self.units).to_base_units()
             else:
diff --git a/pint/testsuite/test_issues.py b/pint/testsuite/test_issues.py
index 4aeae91..958fc0e 100644
--- a/pint/testsuite/test_issues.py
+++ b/pint/testsuite/test_issues.py
@@ -2,6 +2,8 @@
 
 from __future__ import division, unicode_literals, print_function, absolute_import
 
+import math
+
 from pint import UnitRegistry
 from pint.unit import UnitsContainer
 from pint.util import ParserHelper
@@ -427,3 +429,12 @@ class TestIssuesNP(QuantityTestCase):
                 self.assertTrue(False, "ValueError not raised")
             except ValueError:
                 pass
+
+    def test_issue127(self):
+        q = [1., 2., 3., 4.] * self.ureg.meter
+        q[0] = np.nan
+        self.assertNotEqual(q[0], 1.)
+        self.assertTrue(math.isnan(q[0].magnitude))
+        q[1] = float('NaN')
+        self.assertNotEqual(q[1], 2.)
+        self.assertTrue(math.isnan(q[1].magnitude))