Simplify LinExpr.coefficients()

[linpy.git] / linpy / linexprs.py

diff --git a/linpy/linexprs.py b/linpy/linexprs.py
index fce77a6..ab5d344 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')
         """
         if not isinstance(symbol, Symbol):
             raise TypeError('symbol must be a Symbol instance')

-        return Rational(self._coefficients.get(symbol, 0))
+        return self._coefficients.get(symbol, Fraction(0))

 
     __getitem__ = coefficient
 
 
     __getitem__ = coefficient
 


@@ -131,15 +131,14 @@ 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, Rational(coefficient)
+        yield from self._coefficients.items()

 
     @property
     def constant(self):
         """
         The constant term of the expression.
         """
 
     @property
     def constant(self):
         """
         The constant term of the expression.
         """

-        return Rational(self._constant)
+        return self._constant

 
     @property
     def symbols(self):
 
     @property
     def symbols(self):


@@ -180,8 +179,8 @@ class LinExpr:
         term.
         """
         for coefficient in self._coefficients.values():
         term.
         """
         for coefficient in self._coefficients.values():

-            yield Rational(coefficient)
-        yield Rational(self._constant)
+            yield coefficient
+        yield self._constant

 
     def __bool__(self):
         return True
 
     def __bool__(self):
         return True


@@ -411,7 +410,7 @@ class LinExpr:
     @classmethod
     def fromsympy(cls, expr):
         """
     @classmethod
     def fromsympy(cls, expr):
         """

-        Create a linear expression from a sympy expression. Raise ValueError is
+        Create a linear expression from a sympy expression. Raise TypeError is

         the sympy expression is not linear.
         """
         import sympy
         the sympy expression is not linear.
         """
         import sympy


@@ -421,12 +420,18 @@ class LinExpr:
             coefficient = Fraction(coefficient.p, coefficient.q)
             if symbol == sympy.S.One:
                 constant = coefficient
             coefficient = Fraction(coefficient.p, coefficient.q)
             if symbol == sympy.S.One:
                 constant = coefficient

+            elif isinstance(symbol, sympy.Dummy):
+                # we cannot properly convert dummy symbols
+                raise TypeError('cannot convert dummy symbols')

             elif isinstance(symbol, sympy.Symbol):
                 symbol = Symbol(symbol.name)
                 coefficients.append((symbol, coefficient))
             else:
             elif isinstance(symbol, sympy.Symbol):
                 symbol = Symbol(symbol.name)
                 coefficients.append((symbol, coefficient))
             else:

-                raise ValueError('non-linear expression: {!r}'.format(expr))
-        return LinExpr(coefficients, constant)
+                raise TypeError('non-linear expression: {!r}'.format(expr))
+        expr = LinExpr(coefficients, constant)
+        if not isinstance(expr, cls):
+            raise TypeError('cannot convert to a {} instance'.format(cls.__name__))
+        return expr

 
     def tosympy(self):
         """
 
     def tosympy(self):
         """


@@ -507,16 +512,6 @@ class Symbol(LinExpr):
     def _repr_latex_(self):
         return '$${}$$'.format(self.name)
 
     def _repr_latex_(self):
         return '$${}$$'.format(self.name)
 

-    @classmethod
-    def fromsympy(cls, expr):
-        import sympy
-        if isinstance(expr, sympy.Dummy):
-            return Dummy(expr.name)
-        elif isinstance(expr, sympy.Symbol):
-            return Symbol(expr.name)
-        else:
-            raise TypeError('expr must be a sympy.Symbol instance')
-

 
 def symbols(names):
     """
 
 def symbols(names):
     """


@@ -632,13 +627,3 @@ class Rational(LinExpr, Fraction):
         else:
             return '$$\\frac{{{}}}{{{}}}$$'.format(self.numerator,
                 self.denominator)
         else:
             return '$$\\frac{{{}}}{{{}}}$$'.format(self.numerator,
                 self.denominator)

-
-    @classmethod
-    def fromsympy(cls, expr):
-        import sympy
-        if isinstance(expr, sympy.Rational):
-            return Rational(expr.p, expr.q)
-        elif isinstance(expr, numbers.Rational):
-            return Rational(expr)
-        else:
-            raise TypeError('expr must be a sympy.Rational instance')