Fix LinExpr.subs() implementation

[linpy.git] / linpy / linexprs.py

diff --git a/linpy/linexprs.py b/linpy/linexprs.py
index 99ad4ec..b5864e1 100644 (file)
--- a/linpy/linexprs.py
+++ b/linpy/linexprs.py
@@ -131,8 +131,7 @@ class LinExpr:
         Iterate over the pairs (symbol, value) of linear terms in the
         expression. The constant term is ignored.
         """
         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):
 
     @property
     def constant(self):


@@ -179,8 +178,7 @@ class LinExpr:
         Iterate over the coefficient values in the expression, and the constant
         term.
         """
         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):
         yield self._constant
 
     def __bool__(self):


@@ -249,9 +247,10 @@ class LinExpr:
         """
         Test whether two linear expressions are equal.
         """
         """
         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
 
     def __le__(self, other):
         from .polyhedra import Le


@@ -274,9 +273,9 @@ class LinExpr:
         Return the expression multiplied by its lowest common denominator to
         make all values integer.
         """
         Return the expression multiplied by its lowest common denominator to
         make all values integer.
         """

-        lcm = functools.reduce(lambda a, b: a*b // gcd(a, b),
+        lcd = functools.reduce(lambda a, b: a*b // gcd(a, b),

             [value.denominator for value in self.values()])
             [value.denominator for value in self.values()])

-        return self * lcm
+        return self * lcd

 
     def subs(self, symbol, expression=None):
         """
 
     def subs(self, symbol, expression=None):
         """


@@ -295,21 +294,16 @@ class LinExpr:
         2*x + y + 1
         """
         if expression is None:
         2*x + y + 1
         """
         if expression is None:

-            if isinstance(symbol, Mapping):
-                symbol = symbol.items()
-            substitutions = symbol
+            substitutions = dict(symbol)

         else:
         else:

-            substitutions = [(symbol, expression)]
-        result = self
-        for symbol, expression in substitutions:
+            substitutions = {symbol: expression}
+        for symbol in substitutions:

             if not isinstance(symbol, Symbol):
                 raise TypeError('symbols must be Symbol instances')
             if not isinstance(symbol, Symbol):
                 raise TypeError('symbols must be Symbol instances')

-            coefficients = [(othersymbol, coefficient)
-                for othersymbol, coefficient in result._coefficients.items()
-                if othersymbol != symbol]
-            coefficient = result._coefficients.get(symbol, 0)
-            constant = result._constant
-            result = LinExpr(coefficients, constant) + coefficient*expression
+        result = self._constant
+        for symbol, coefficient in self._coefficients.items():
+            expression = substitutions.get(symbol, symbol)
+            result += coefficient * expression

         return result
 
     @classmethod
         return result
 
     @classmethod


@@ -499,7 +493,9 @@ class Symbol(LinExpr):
         return True
 
     def __eq__(self, other):
         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):
         """
 
     def asdummy(self):
         """