Improve error messages in linexprs.py

diff --git a/pypol/linexprs.py b/pypol/linexprs.py
index e73449e..229e8d9 100644 (file)
--- a/pypol/linexprs.py
+++ b/pypol/linexprs.py
@@ -44,11 +44,11 @@ class Expression:
             if not isinstance(symbol, Symbol):
                 raise TypeError('symbols must be Symbol instances')
             if not isinstance(coefficient, numbers.Rational):
-                raise TypeError('coefficients must be Rational instances')
+                raise TypeError('coefficients must be rational numbers')
         coefficients = [(symbol, Fraction(coefficient))
             for symbol, coefficient in coefficients if coefficient != 0]
         if not isinstance(constant, numbers.Rational):
-            raise TypeError('constant must be a Rational instance')
+            raise TypeError('constant must be a rational number')
         constant = Fraction(constant)
         if len(coefficients) == 0:
             return Rational(constant)