X-Git-Url: https://scm.cri.ensmp.fr/git/linpy.git/blobdiff_plain/4af78812d25b28cee283e671c0bd5944133b6ce5..a93fd1cb792ef6dafaeb2599823256241c061cd3:/linpy/linexprs.py

diff --git a/linpy/linexprs.py b/linpy/linexprs.py
index a49f90e..d2554a0 100644
--- a/linpy/linexprs.py
+++ b/linpy/linexprs.py
@@ -294,21 +294,16 @@ class LinExpr:
         2*x + y + 1
         """
         if expression is None:
-            if isinstance(symbol, Mapping):
-                symbol = symbol.items()
-            substitutions = symbol
+            substitutions = dict(symbol)
         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')
-            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
@@ -336,7 +331,7 @@ class LinExpr:
                 return left / right
         raise SyntaxError('invalid syntax')
 
-    _RE_NUM_VAR = re.compile(r'(\d+|\))\s*([^\W\d_]\w*|\()')
+    _RE_NUM_VAR = re.compile(r'(\d+|\))\s*([^\W\d]\w*|\()')
 
     @classmethod
     def fromstring(cls, string):
@@ -344,7 +339,7 @@ class LinExpr:
         Create an expression from a string. Raise SyntaxError if the string is
         not properly formatted.
         """
-        # add implicit multiplication operators, e.g. '5x' -> '5*x'
+        # Add implicit multiplication operators, e.g. '5x' -> '5*x'.
         string = LinExpr._RE_NUM_VAR.sub(r'\1*\2', string)
         tree = ast.parse(string, 'eval')
         expr = cls._fromast(tree)
@@ -421,7 +416,8 @@ class LinExpr:
             if symbol == sympy.S.One:
                 constant = coefficient
             elif isinstance(symbol, sympy.Dummy):
-                # we cannot properly convert dummy symbols
+                # We cannot properly convert dummy symbols with respect to
+                # symbol equalities.
                 raise TypeError('cannot convert dummy symbols')
             elif isinstance(symbol, sympy.Symbol):
                 symbol = Symbol(symbol.name)
@@ -455,6 +451,13 @@ class Symbol(LinExpr):
     Two instances of Symbol are equal if they have the same name.
     """
 
+    __slots__ = (
+        '_name',
+        '_constant',
+        '_symbols',
+        '_dimension',
+    )
+
     def __new__(cls, name):
         """
         Return a symbol with the name string given in argument.
@@ -468,12 +471,17 @@ class Symbol(LinExpr):
             raise SyntaxError('invalid syntax')
         self = object().__new__(cls)
         self._name = name
-        self._coefficients = {self: Fraction(1)}
         self._constant = Fraction(0)
         self._symbols = (self,)
         self._dimension = 1
         return self
 
+    @property
+    def _coefficients(self):
+        # This is not implemented as an attribute, because __hash__ is not
+        # callable in __new__ in class Dummy.
+        return {self: Fraction(1)}
+
     @property
     def name(self):
         """
@@ -558,15 +566,8 @@ class Dummy(Symbol):
         """
         if name is None:
             name = 'Dummy_{}'.format(Dummy._count)
-        elif not isinstance(name, str):
-            raise TypeError('name must be a string')
-        self = object().__new__(cls)
+        self = super().__new__(cls, name)
         self._index = Dummy._count
-        self._name = name.strip()
-        self._coefficients = {self: Fraction(1)}
-        self._constant = Fraction(0)
-        self._symbols = (self,)
-        self._dimension = 1
         Dummy._count += 1
         return self
 
@@ -591,6 +592,13 @@ class Rational(LinExpr, Fraction):
     fractions.Fraction classes.
     """
 
+    __slots__ = (
+        '_coefficients',
+        '_constant',
+        '_symbols',
+        '_dimension',
+    ) + Fraction.__slots__
+
     def __new__(cls, numerator=0, denominator=None):
         self = object().__new__(cls)
         self._coefficients = {}