Better implementation of NSAD'10 example

[linpy.git] / pypol / linexprs.py

diff --git a/pypol/linexprs.py b/pypol/linexprs.py
index ccd1564..f3cff23 100644 (file)
--- a/pypol/linexprs.py
+++ b/pypol/linexprs.py
@@ -9,8 +9,8 @@ from fractions import Fraction, gcd
 
 __all__ = [
     'Expression',
-    'Symbol', 'symbols',
-    'Constant',
+    'Symbol', 'symbols', 'Dummy',
+    'Rational',
 ]
 
 
@@ -20,7 +20,7 @@ def _polymorphic(func):
         if isinstance(right, Expression):
             return func(left, right)
         elif isinstance(right, numbers.Rational):
-            right = Constant(right)
+            right = Rational(right)
             return func(left, right)
         return NotImplemented
     return wrapper
@@ -44,7 +44,7 @@ class Expression:
                 raise TypeError('too many arguments')
             return Expression.fromstring(coefficients)
         if coefficients is None:
-            return Constant(constant)
+            return Rational(constant)
         if isinstance(coefficients, dict):
             coefficients = coefficients.items()
         for symbol, coefficient in coefficients:
@@ -53,7 +53,7 @@ class Expression:
         coefficients = [(symbol, coefficient)
             for symbol, coefficient in coefficients if coefficient != 0]
         if len(coefficients) == 0:
-            return Constant(constant)
+            return Rational(constant)
         if len(coefficients) == 1 and constant == 0:
             symbol, coefficient = coefficients[0]
             if coefficient == 1:
@@ -61,18 +61,18 @@ class Expression:
         self = object().__new__(cls)
         self._coefficients = OrderedDict()
         for symbol, coefficient in sorted(coefficients,
-                key=lambda item: item[0].name):
-            if isinstance(coefficient, Constant):
+                key=lambda item: item[0].sortkey()):
+            if isinstance(coefficient, Rational):
                 coefficient = coefficient.constant
             if not isinstance(coefficient, numbers.Rational):
                 raise TypeError('coefficients must be rational numbers '
-                    'or Constant instances')
+                    'or Rational instances')
             self._coefficients[symbol] = coefficient
-        if isinstance(constant, Constant):
+        if isinstance(constant, Rational):
             constant = constant.constant
         if not isinstance(constant, numbers.Rational):
             raise TypeError('constant must be a rational number '
-                'or a Constant instance')
+                'or a Rational instance')
         self._constant = constant
         self._symbols = tuple(self._coefficients)
         self._dimension = len(self._symbols)
@@ -127,7 +127,7 @@ class Expression:
 
     @_polymorphic
     def __add__(self, other):
-        coefficients = defaultdict(Constant, self.coefficients())
+        coefficients = defaultdict(Rational, self.coefficients())
         for symbol, coefficient in other.coefficients():
             coefficients[symbol] += coefficient
         constant = self.constant + other.constant
@@ -137,7 +137,7 @@ class Expression:
 
     @_polymorphic
     def __sub__(self, other):
-        coefficients = defaultdict(Constant, self.coefficients())
+        coefficients = defaultdict(Rational, self.coefficients())
         for symbol, coefficient in other.coefficients():
             coefficients[symbol] -= coefficient
         constant = self.constant - other.constant
@@ -166,8 +166,8 @@ class Expression:
         if other.isconstant():
             coefficients = dict(self.coefficients())
             for symbol in coefficients:
-                coefficients[symbol] = Constant(coefficients[symbol], other.constant)
-            constant = Constant(self.constant, other.constant)
+                coefficients[symbol] = Rational(coefficients[symbol], other.constant)
+            constant = Rational(self.constant, other.constant)
             return Expression(coefficients, constant)
         if isinstance(other, Expression):
             raise ValueError('non-linear expression: '
@@ -177,7 +177,7 @@ class Expression:
     def __rtruediv__(self, other):
         if isinstance(other, self):
             if self.isconstant():
-                return Constant(other, self.constant)
+                return Rational(other, self.constant)
             else:
                 raise ValueError('non-linear expression: '
                         '{} / {}'.format(other._parenstr(), self._parenstr()))
@@ -242,7 +242,7 @@ class Expression:
         elif isinstance(node, ast.Name):
             return Symbol(node.id)
         elif isinstance(node, ast.Num):
-            return Constant(node.n)
+            return Rational(node.n)
         elif isinstance(node, ast.UnaryOp) and isinstance(node.op, ast.USub):
             return -cls._fromast(node.operand)
         elif isinstance(node, ast.BinOp):
@@ -355,7 +355,7 @@ class Symbol(Expression):
         return self._name
 
     def __hash__(self):
-        return hash(self._name)
+        return hash(self.sortkey())
 
     def coefficient(self, symbol):
         if not isinstance(symbol, Symbol):
@@ -380,6 +380,9 @@ class Symbol(Expression):
     def dimension(self):
         return 1
 
+    def sortkey(self):
+        return self.name,
+
     def issymbol(self):
         return True
 
@@ -387,7 +390,11 @@ class Symbol(Expression):
         yield 1
 
     def __eq__(self, other):
-        return isinstance(other, Symbol) and self.name == other.name
+        return not isinstance(other, Dummy) and isinstance(other, Symbol) \
+            and self.name == other.name
+
+    def asdummy(self):
+        return Dummy(self.name)
 
     @classmethod
     def _fromast(cls, node):
@@ -414,7 +421,35 @@ def symbols(names):
     return tuple(Symbol(name) for name in names)
 
 
-class Constant(Expression):
+class Dummy(Symbol):
+
+    __slots__ = (
+        '_name',
+        '_index',
+    )
+
+    _count = 0
+
+    def __new__(cls, name=None):
+        if name is None:
+            name = 'Dummy_{}'.format(Dummy._count)
+        self = object().__new__(cls)
+        self._name = name.strip()
+        self._index = Dummy._count
+        Dummy._count += 1
+        return self
+
+    def __hash__(self):
+        return hash(self.sortkey())
+
+    def sortkey(self):
+        return self._name, self._index
+
+    def __eq__(self, other):
+        return isinstance(other, Dummy) and self._index == other._index
+
+
+class Rational(Expression):
 
     __slots__ = (
         '_constant',
@@ -422,7 +457,7 @@ class Constant(Expression):
 
     def __new__(cls, numerator=0, denominator=None):
         self = object().__new__(cls)
-        if denominator is None and isinstance(numerator, Constant):
+        if denominator is None and isinstance(numerator, Rational):
             self._constant = numerator.constant
         else:
             self._constant = Fraction(numerator, denominator)
@@ -455,7 +490,7 @@ class Constant(Expression):
 
     @_polymorphic
     def __eq__(self, other):
-        return isinstance(other, Constant) and self.constant == other.constant
+        return isinstance(other, Rational) and self.constant == other.constant
 
     def __bool__(self):
         return self.constant != 0
@@ -464,14 +499,14 @@ class Constant(Expression):
     def fromstring(cls, string):
         if not isinstance(string, str):
             raise TypeError('string must be a string instance')
-        return Constant(Fraction(string))
+        return Rational(Fraction(string))
 
     @classmethod
     def fromsympy(cls, expr):
         import sympy
         if isinstance(expr, sympy.Rational):
-            return Constant(expr.p, expr.q)
+            return Rational(expr.p, expr.q)
         elif isinstance(expr, numbers.Rational):
-            return Constant(expr)
+            return Rational(expr)
         else:
             raise TypeError('expr must be a sympy.Rational instance')