Fix Symbol == LinExpr comparisons

[linpy.git] / linpy / linexprs.py

diff --git a/linpy/linexprs.py b/linpy/linexprs.py
index b2cec53..e4ed1cc 100644 (file)
--- a/linpy/linexprs.py
+++ b/linpy/linexprs.py
@@ -122,7 +122,7 @@ class LinExpr:
         """
         if not isinstance(symbol, Symbol):
             raise TypeError('symbol must be a Symbol instance')
-        return self._coefficients.get(symbol, 0)
+        return self._coefficients.get(symbol, Fraction(0))
 
     __getitem__ = coefficient
 
@@ -131,8 +131,7 @@ class LinExpr:
         Iterate over the pairs (symbol, value) of linear terms in the
         expression. The constant term is ignored.
         """
-        for symbol, coefficient in self._coefficients.items():
-            yield symbol, coefficient
+        yield from self._coefficients.items()
 
     @property
     def constant(self):
@@ -179,8 +178,7 @@ class LinExpr:
         Iterate over the coefficient values in the expression, and the constant
         term.
         """
-        for coefficient in self._coefficients.values():
-            yield coefficient
+        yield from self._coefficients.values()
         yield self._constant
 
     def __bool__(self):
@@ -249,9 +247,10 @@ class LinExpr:
         """
         Test whether two linear expressions are equal.
         """
-        return isinstance(other, LinExpr) and \
-            self._coefficients == other._coefficients and \
-            self._constant == other._constant
+        if isinstance(other, LinExpr):
+            return self._coefficients == other._coefficients and \
+                self._constant == other._constant
+        return NotImplemented
 
     def __le__(self, other):
         from .polyhedra import Le
@@ -499,7 +498,9 @@ class Symbol(LinExpr):
         return True
 
     def __eq__(self, other):
-        return self.sortkey() == other.sortkey()
+        if isinstance(other, Symbol):
+            return self.sortkey() == other.sortkey()
+        return NotImplemented
 
     def asdummy(self):
         """