diff --git a/dagrt/codegen/expressions.py b/dagrt/codegen/expressions.py
index 6f530ad7e304de626a6e00148f4b75f9bf5bec17..249abbc80d6e298585b285c6e764bbc534179b3f 100644
--- a/dagrt/codegen/expressions.py
+++ b/dagrt/codegen/expressions.py
@@ -36,7 +36,7 @@ class FortranExpressionMapper(StringifyMapper):
         """name_manager is a map from a variable name (as a string) to its
         representation (as a string).
         """
-        super(FortranExpressionMapper, self).__init__(repr)
+        super(FortranExpressionMapper, self).__init__()
         self._name_manager = name_manager
 
     def map_constant(self, expr, enclosing_prec):
@@ -128,13 +128,6 @@ class FortranExpressionMapper(StringifyMapper):
 
 # {{{ python
 
-def _map_python_constant(constant):
-    if isinstance(constant, (float, np.number)):
-        if np.isinf(constant) or np.isnan(constant):
-            return "float('" + repr(constant) + "')"
-    return repr(constant)
-
-
 class PythonExpressionMapper(StringifyMapper):
     """Converts expressions to Python code."""
 
@@ -145,11 +138,17 @@ class PythonExpressionMapper(StringifyMapper):
 
         numpy is the name of the numpy module.
         """
-        super(PythonExpressionMapper, self).__init__(_map_python_constant)
+        super(PythonExpressionMapper, self).__init__()
         self._name_manager = name_manager
         self._function_registry = function_registry
         self._numpy = numpy
 
+    def map_constant(self, expr, *args):
+        if isinstance(expr, (float, np.number)):
+            if np.isinf(expr) or np.isnan(expr):
+                return "float('" + repr(expr) + "')"
+        return repr(expr)
+
     def map_foreign(self, expr, *args):
         if expr is None:
             return "None"