Merge 0e5a81b into 002c889

essm/variables/_core.py

@@ -26,9 +26,8 @@
 import six
 from sympy import Basic, S
 from sympy.physics.units import Dimension, Quantity
-# FIXME use SymPy 1.1
-# from sympy.physics.units.quantities import \
-#     _Quantity_constructor_postprocessor_Add
+from sympy.physics.units.quantities import \
+    _Quantity_constructor_postprocessor_Add
 
 from .units import derive_unit
 from ..bases import RegistryType
@@ -135,31 +134,7 @@ def __doc__(self):
         return self.definition.__doc__
 
 
-def _Quantity_constructor_postprocessor_Add(expr):
-    # Construction postprocessor for the addition,
-    # checks for dimension mismatches of the addends, thus preventing
-    # expressions like `meter + second` to be created.
-
-    deset = {
-        tuple(
-            sorted(
-                Dimension(Quantity.get_dimensional_expr(i))
-                .get_dimensional_dependencies().items()))
-        for i in expr.args
-        if i.free_symbols == set() and  # do not raise if there are symbols
-        # (free symbols could contain the units corrections)
-        not i.is_number}
-    # If `deset` has more than one element, then some dimensions do not
-    # match in the sum:
-    if len(deset) > 1:
-        raise ValueError("summation of quantities of incompatible dimensions")
-    return expr
-
-
-Basic._constructor_postprocessor_mapping[Quantity] = {
-    "Add": [_Quantity_constructor_postprocessor_Add], }
-
 Basic._constructor_postprocessor_mapping[BaseVariable] = {
-    "Add": [_Quantity_constructor_postprocessor_Add], }
+     "Add": [_Quantity_constructor_postprocessor_Add], }
 
 __all__ = ('Variable', )

essm/variables/units.py

@@ -60,11 +60,12 @@ def derive_quantity(expr, name=None):
 
 def derive_unit(expr, name=None):
     """Derive SI-unit from an expression, omitting scale factors."""
+    from sympy.physics.units.dimensions import dimsys_SI
     dim = Dimension(Quantity.get_dimensional_expr(expr))
     return functools.reduce(
         operator.mul, (
             SI_DIMENSIONS[d] ** p
-            for d, p in Dimension.get_dimensional_dependencies(dim).items()),
+            for d, p in dimsys_SI.get_dimensional_dependencies(dim).items()),
         1)