Add abstract class GeometricObject

[linpy.git] / pypol / linexprs.py

diff --git a/pypol/linexprs.py b/pypol/linexprs.py
index a9f188b..5ec5efd 100644 (file)
--- a/pypol/linexprs.py
+++ b/pypol/linexprs.py
@@ -3,7 +3,7 @@ import functools
 import numbers
 import re
 
-from collections import OrderedDict, defaultdict
+from collections import OrderedDict, defaultdict, Mapping
 from fractions import Fraction, gcd
 
 
@@ -45,7 +45,7 @@ class Expression:
             return Expression.fromstring(coefficients)
         if coefficients is None:
             return Rational(constant)
-        if isinstance(coefficients, dict):
+        if isinstance(coefficients, Mapping):
             coefficients = coefficients.items()
         for symbol, coefficient in coefficients:
             if not isinstance(symbol, Symbol):
@@ -218,7 +218,7 @@ class Expression:
 
     def subs(self, symbol, expression=None):
         if expression is None:
-            if isinstance(symbol, dict):
+            if isinstance(symbol, Mapping):
                 symbol = symbol.items()
             substitutions = symbol
         else: