Fixed problem with uncertainties

When adding two measurements the error is different if both
measurements are the same versus if they are different. For this
testing M1 is M2 must give true. This was not the case because
a new object was created for M2 when converting.

1 files changed, 7 insertions, 2 deletions

diff --git a/pint/quantity.py b/pint/quantity.py
index 2e2596e..509c0a3 100644
--- a/pint/quantity.py
+++ b/pint/quantity.py
@@ -318,8 +318,10 @@ class _Quantity(object):
 
         # Presence of non-multiplicative units gives rise to several cases.
         if is_self_multiplicative and is_other_multiplicative:
+            if self._units == other._units:
+                self._magnitude = op(self._magnitude, other._magnitude)
             # If only self has a delta unit, other determines unit of result.
-            if self._get_delta_units() and not other._get_delta_units():
+            elif self._get_delta_units() and not other._get_delta_units():
                 self._magnitude = op(self._convert_magnitude(other.units),
                                      other._magnitude)
                 self._units = copy.copy(other.units)
@@ -412,8 +414,11 @@ class _Quantity(object):
 
         # Presence of non-multiplicative units gives rise to several cases.
         if is_self_multiplicative and is_other_multiplicative:
+            if self._units == other._units:
+                magnitude = op(self._magnitude, other._magnitude)
+                units = copy.copy(self.units)
             # If only self has a delta unit, other determines unit of result.
-            if self._get_delta_units() and not other._get_delta_units():
+            elif self._get_delta_units() and not other._get_delta_units():
                 magnitude = op(self._convert_magnitude(other.units),
                                other._magnitude)
                 units = copy.copy(other.units)