Better implementation of symbols and constants

[linpy.git] / pypol / linexprs.py

diff --git a/pypol/linexprs.py b/pypol/linexprs.py
index 0db7edd..9449219 100644 (file)
--- a/pypol/linexprs.py
+++ b/pypol/linexprs.py
@@ -3,6 +3,7 @@ import functools
 import numbers
 import re
 
+from collections import OrderedDict
 from fractions import Fraction, gcd
 
 
@@ -35,6 +36,7 @@ class Expression:
         '_constant',
         '_symbols',
         '_dimension',
+        '_hash',
     )
 
     def __new__(cls, coefficients=None, constant=0):
@@ -67,19 +69,21 @@ class Expression:
                 raise TypeError('coefficients must be rational numbers '
                     'or Constant instances')
             self._coefficients[symbol] = coefficient
+        self._coefficients = OrderedDict(sorted(self._coefficients.items()))
         if isinstance(constant, Constant):
             constant = constant.constant
         if not isinstance(constant, numbers.Rational):
             raise TypeError('constant must be a rational number '
                 'or a Constant instance')
         self._constant = constant
-        self._symbols = tuple(sorted(self._coefficients))
+        self._symbols = tuple(self._coefficients)
         self._dimension = len(self._symbols)
+        self._hash = hash((tuple(self._coefficients.items()), self._constant))
         return self
 
     def coefficient(self, symbol):
         if isinstance(symbol, Symbol):
-            symbol = str(symbol)
+            symbol = symbol.name
         elif not isinstance(symbol, str):
             raise TypeError('symbol must be a string or a Symbol instance')
         try:
@@ -90,8 +94,7 @@ class Expression:
     __getitem__ = coefficient
 
     def coefficients(self):
-        for symbol in self.symbols:
-            yield symbol, self.coefficient(symbol)
+        yield from self._coefficients.items()
 
     @property
     def constant(self):
@@ -105,6 +108,9 @@ class Expression:
     def dimension(self):
         return self._dimension
 
+    def __hash__(self):
+        return self._hash
+
     def isconstant(self):
         return False
 
@@ -219,9 +225,6 @@ class Expression:
         from .polyhedra import Gt
         return Gt(self, other)
 
-    def __hash__(self):
-        return hash((tuple(sorted(self._coefficients.items())), self._constant))
-
     def _toint(self):
         lcm = functools.reduce(lambda a, b: a*b // gcd(a, b),
             [value.denominator for value in self.values()])
@@ -252,9 +255,12 @@ class Expression:
                 return left / right
         raise SyntaxError('invalid syntax')
 
+    _RE_NUM_VAR = re.compile(r'(\d+|\))\s*([^\W\d_]\w*|\()')
+
     @classmethod
     def fromstring(cls, string):
-        string = re.sub(r'(\d+|\))\s*([^\W\d_]\w*|\()', r'\1*\2', string)
+        # add implicit multiplication operators, e.g. '5x' -> '5*x'
+        string = cls._RE_NUM_VAR.sub(r'\1*\2', string)
         tree = ast.parse(string, 'eval')
         return cls._fromast(tree)
 
@@ -333,8 +339,9 @@ class Expression:
 
 class Symbol(Expression):
 
-    __slots__ = Expression.__slots__ + (
+    __slots__ = (
         '_name',
+        '_hash',
     )
 
     def __new__(cls, name):
@@ -344,20 +351,48 @@ class Symbol(Expression):
             raise TypeError('name must be a string or a Symbol instance')
         name = name.strip()
         self = object().__new__(cls)
-        self._coefficients = {name: 1}
-        self._constant = 0
-        self._symbols = tuple(name)
         self._name = name
-        self._dimension = 1
+        self._hash = hash(self._name)
         return self
 
     @property
     def name(self):
         return self._name
 
+    def __hash__(self):
+        return self._hash
+
+    def coefficient(self, symbol):
+        if isinstance(symbol, Symbol):
+            symbol = symbol.name
+        elif not isinstance(symbol, str):
+            raise TypeError('symbol must be a string or a Symbol instance')
+        if symbol == self.name:
+            return 1
+        else:
+            return 0
+
+    def coefficients(self):
+        yield self.name, 1
+
+    @property
+    def constant(self):
+        return 0
+
+    @property
+    def symbols(self):
+        return self.name,
+
+    @property
+    def dimension(self):
+        return 1
+
     def issymbol(self):
         return True
 
+    def __eq__(self, other):
+        return isinstance(other, Symbol) and self.name == other.name
+
     @classmethod
     def _fromast(cls, node):
         if isinstance(node, ast.Module) and len(node.body) == 1:
@@ -388,20 +423,48 @@ def symbols(names):
 
 class Constant(Expression):
 
+    __slots__ = (
+        '_constant',
+        '_hash',
+    )
+
     def __new__(cls, numerator=0, denominator=None):
         self = object().__new__(cls)
         if denominator is None and isinstance(numerator, Constant):
             self._constant = numerator.constant
         else:
             self._constant = Fraction(numerator, denominator)
-        self._coefficients = {}
-        self._symbols = ()
-        self._dimension = 0
+        self._hash = hash(self._constant)
         return self
 
+    def __hash__(self):
+        return self._hash
+
+    def coefficient(self, symbol):
+        if isinstance(symbol, Symbol):
+            symbol = symbol.name
+        elif not isinstance(symbol, str):
+            raise TypeError('symbol must be a string or a Symbol instance')
+        return 0
+
+    def coefficients(self):
+        yield from []
+
+    @property
+    def symbols(self):
+        return ()
+
+    @property
+    def dimension(self):
+        return 0
+
     def isconstant(self):
         return True
 
+    @_polymorphic
+    def __eq__(self, other):
+        return isinstance(other, Constant) and self.constant == other.constant
+
     def __bool__(self):
         return self.constant != 0