Merge 80b7fba into fa449cb

essm/variables/utils.py

@@ -54,12 +54,12 @@ def extract_variables(expr):
 
 
 def replace_variables(expr, variables=None):
-    """Replace all base variables in expression."""
+    """Replace all base variables in expression by ``variables``."""
     if not isinstance(expr, Expr):  # stop recursion
         return expr
 
     variables = {
-        key._name: replace_variables(value)
+        getattr(key, '_name', key): replace_variables(value)
         for key, value in (variables or {}).items()}
 
     return expr.replace(

tests/test_equations.py

@@ -2,7 +2,7 @@
 """Test equations."""
 
 import pytest
-from sympy import S
+from sympy import S, Symbol
 
 from essm import Eq
 from essm._generator import EquationWriter
@@ -68,6 +68,7 @@ def test_variable_replacement():
     """Test replace variables by values and symbols in expression."""
     expr = demo_fall.rhs
     vdict = Variable.__defaults__.copy()
+    vdict[Symbol('x')] = 1
     assert replace_variables(expr, vdict) == \
         4.9 * demo_fall.definition.t._name ** 2