X-Git-Url: https://svn.cri.ensmp.fr/git/linpy.git/blobdiff_plain/4162c0430092e0ba2b8d8d62b5de24cdd71abe3b..HEAD:/linpy/linexprs.py

diff --git a/linpy/linexprs.py b/linpy/linexprs.py
index 3c00f22..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
@@ -405,10 +410,12 @@ class LinExpr:
                 symbol = Symbol(symbol.name)
                 coefficients.append((symbol, coefficient))
             else:
-                raise TypeError('non-linear expression: {!r}'.format(expression))
+                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__))
+            raise TypeError('cannot convert to a {} instance'.format(
+                cls.__name__))
         return expression
 
     def tosympy(self):