X-Git-Url: https://scm.cri.ensmp.fr/git/linpy.git/blobdiff_plain/2b13a146860ac116ce0388d8f7551044c09c55f7..d585b06ccf67b2837519f4b48c6800dcdb924d9d:/linpy/linexprs.py?ds=sidebyside

diff --git a/linpy/linexprs.py b/linpy/linexprs.py
index ee6e39e..ccfbbfa 100644
--- a/linpy/linexprs.py
+++ b/linpy/linexprs.py
@@ -20,14 +20,16 @@ import functools
 import numbers
 import re
 
-from collections import OrderedDict, defaultdict, Mapping
+from collections import defaultdict, Mapping, OrderedDict
 from fractions import Fraction, gcd
 
 
 __all__ = [
+    'Dummy',
     'LinExpr',
-    'Symbol', 'Dummy', 'symbols',
     'Rational',
+    'Symbol',
+    'symbols',
 ]
 
 
@@ -59,8 +61,8 @@ class LinExpr:
     def __new__(cls, coefficients=None, constant=0):
         """
         Return a linear expression from a dictionary or a sequence, that maps
-        symbols to their coefficients, and a constant term. The coefficients and
-        the constant term must be rational numbers.
+        symbols to their coefficients, and a constant term. The coefficients
+        and the constant term must be rational numbers.
 
         For example, the linear expression x + 2*y + 1 can be constructed using
         one of the following instructions:
@@ -79,9 +81,9 @@ class LinExpr:
         >>> LinExpr('x + 2y + 1')
 
         A linear expression with a single symbol of coefficient 1 and no
-        constant term is automatically subclassed as a Symbol instance. A linear
-        expression with no symbol, only a constant term, is automatically
-        subclassed as a Rational instance.
+        constant term is automatically subclassed as a Symbol instance. A
+        linear expression with no symbol, only a constant term, is
+        automatically subclassed as a Rational instance.
         """
         if isinstance(coefficients, str):
             if constant != 0:
@@ -105,8 +107,9 @@ class LinExpr:
             symbol, coefficient = coefficients[0]
             if coefficient == 1:
                 return symbol
-        coefficients = [(symbol, Fraction(coefficient))
-            for symbol, coefficient in coefficients if coefficient != 0]
+        coefficients = [(symbol_, Fraction(coefficient_))
+                        for symbol_, coefficient_ in coefficients
+                        if coefficient_ != 0]
         coefficients.sort(key=lambda item: item[0].sortkey())
         self = object().__new__(cls)
         self._coefficients = OrderedDict(coefficients)
@@ -223,7 +226,8 @@ class LinExpr:
         Return the product of the linear expression by a rational.
         """
         if isinstance(other, numbers.Rational):
-            coefficients = ((symbol, coefficient * other)
+            coefficients = (
+                (symbol, coefficient * other)
                 for symbol, coefficient in self._coefficients.items())
             constant = self._constant * other
             return LinExpr(coefficients, constant)
@@ -236,7 +240,8 @@ class LinExpr:
         Return the quotient of the linear expression by a rational.
         """
         if isinstance(other, numbers.Rational):
-            coefficients = ((symbol, coefficient / other)
+            coefficients = (
+                (symbol, coefficient / other)
                 for symbol, coefficient in self._coefficients.items())
             constant = self._constant / other
             return LinExpr(coefficients, constant)
@@ -280,7 +285,7 @@ class LinExpr:
         make all values integer.
         """
         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 * lcd
 
     def subs(self, symbol, expression=None):
@@ -306,7 +311,7 @@ class LinExpr:
         for symbol in substitutions:
             if not isinstance(symbol, Symbol):
                 raise TypeError('symbols must be Symbol instances')
-        result = self._constant
+        result = Rational(self._constant)
         for symbol, coefficient in self._coefficients.items():
             expression = substitutions.get(symbol, symbol)
             result += coefficient * expression
@@ -348,10 +353,10 @@ class LinExpr:
         # 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)
-        if not isinstance(expr, cls):
+        expression = cls._fromast(tree)
+        if not isinstance(expression, cls):
             raise SyntaxError('invalid syntax')
-        return expr
+        return expression
 
     def __repr__(self):
         string = ''
@@ -385,7 +390,7 @@ class LinExpr:
             return '({})'.format(string)
 
     @classmethod
-    def fromsympy(cls, expr):
+    def fromsympy(cls, expression):
         """
         Create a linear expression from a SymPy expression. Raise TypeError is
         the sympy expression is not linear.
@@ -393,7 +398,7 @@ class LinExpr:
         import sympy
         coefficients = []
         constant = 0
-        for symbol, coefficient in expr.as_coefficients_dict().items():
+        for symbol, coefficient in expression.as_coefficients_dict().items():
             coefficient = Fraction(coefficient.p, coefficient.q)
             if symbol == sympy.S.One:
                 constant = coefficient
@@ -405,23 +410,25 @@ class LinExpr:
                 symbol = Symbol(symbol.name)
                 coefficients.append((symbol, coefficient))
             else:
-                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
+                raise TypeError('non-linear expression: {!r}'.format(
+                    expression))
+        expression = LinExpr(coefficients, constant)
+        if not isinstance(expression, cls):
+            raise TypeError('cannot convert to a {} instance'.format(
+                cls.__name__))
+        return expression
 
     def tosympy(self):
         """
         Convert the linear expression to a SymPy expression.
         """
         import sympy
-        expr = 0
+        expression = 0
         for symbol, coefficient in self.coefficients():
             term = coefficient * sympy.Symbol(symbol.name)
-            expr += term
-        expr += self.constant
-        return expr
+            expression += term
+        expression += self.constant
+        return expression
 
 
 class Symbol(LinExpr):