diff --git a/pymath/calculus/operator/par.py b/pymath/calculus/operator/par.py
index 4977c58..6d07969 100644
--- a/pymath/calculus/operator/par.py
+++ b/pymath/calculus/operator/par.py
@@ -4,24 +4,22 @@
 
 from .operator import Operator
 
+
 class Par(Operator):
 
     """ The operator ( """
 
     _CARACT = {
-        "operator" : "(", \
-        "name" : "par",\
-        "priority" : 0, \
-        "arity" : 0, \
+        "operator": "(",
+        "name": "par",
+        "priority": 0,
+        "arity": 0,
     }
 
     def __init__(self):
         """ Initiate Par Operator """
         super(Par, self).__init__(**self._CARACT)
 
-
-
-
 # -----------------------------
 # Reglages pour 'vim'
 # vim:set autoindent expandtab tabstop=4 shiftwidth=4:
diff --git a/pymath/calculus/operator/pw.py b/pymath/calculus/operator/pw.py
index 5d2d1d3..1b83d65 100644
--- a/pymath/calculus/operator/pw.py
+++ b/pymath/calculus/operator/pw.py
@@ -5,6 +5,7 @@
 from .operator import Operator
 from ..generic import flatten_list
 
+
 class Pw(Operator):
 
     """ The operator ^
@@ -29,13 +30,13 @@ class Pw(Operator):
     """
 
     _CARACT = {
-        "operator" : "^", \
-        "name" : "pw",\
-        "priority" : 6, \
-        "arity" : 2, \
-        "actions" : ("__pow__",""), \
-        "txt" :  "{op1} ^ {op2}",\
-        "tex" :  "{op1}^{{  {op2} }}",\
+        "operator": "^",
+        "name": "pw",
+        "priority": 6,
+        "arity": 2,
+        "actions": ("__pow__", ""),
+        "txt":  "{op1} ^ {op2}",
+        "tex":  "{op1}^{{  {op2} }}",
     }
 
     def __init__(self):
@@ -52,7 +53,7 @@ class Pw(Operator):
         try:
             if opl.mainOp.priority < self.priority:
                 ans = flatten_list(["(", opl, ")"])
-        except AttributeError as e:
+        except AttributeError:
             # op has not the attribute priority
             pass
         try:
@@ -75,7 +76,7 @@ class Pw(Operator):
         """
         op1 = self.l_parenthesis(args[0], True)
         op2 = args[1]
-        ans = self.tex.format(op1 = op1, op2 = op2)
+        ans = self.tex.format(op1=op1, op2=op2)
 
         return ans
 
diff --git a/pymath/calculus/operator/sub.py b/pymath/calculus/operator/sub.py
index 4dd7c7f..2bc2c8c 100644
--- a/pymath/calculus/operator/sub.py
+++ b/pymath/calculus/operator/sub.py
@@ -5,6 +5,7 @@
 from .operator import Operator
 from ..generic import flatten_list
 
+
 class Sub(Operator):
 
     """ The operator -
@@ -28,13 +29,13 @@ class Sub(Operator):
     '-1 - 2'
     """
     _CARACT = {
-        "operator" : "-", \
-        "name" : "sub",\
-        "priority" : 2, \
-        "arity" : 2, \
-        "actions" : ("__sub__","__rsub__"), \
-        "txt" :  "{op1} - {op2}",\
-        "tex" :  "{op1} - {op2}",\
+        "operator": "-",
+        "name": "sub",
+        "priority": 2,
+        "arity": 2,
+        "actions": ("__sub__", "__rsub__"),
+        "txt":  "{op1} - {op2}",
+        "tex":  "{op1} - {op2}",
         }
 
     def __init__(self):
@@ -62,12 +63,6 @@ class Sub(Operator):
             ans = ' '.join([str(i) for i in ans])
         return ans
 
-
-
-
-
-
-
 # -----------------------------
 # Reglages pour 'vim'
 # vim:set autoindent expandtab tabstop=4 shiftwidth=4:
diff --git a/pymath/calculus/operator/sub1.py b/pymath/calculus/operator/sub1.py
index 49ccd2e..e4e9447 100644
--- a/pymath/calculus/operator/sub1.py
+++ b/pymath/calculus/operator/sub1.py
@@ -5,6 +5,7 @@
 from .operator import Operator
 from ..generic import flatten_list
 
+
 class Sub1(Operator):
 
     """ The operator -
@@ -25,13 +26,13 @@ class Sub1(Operator):
     """
 
     _CARACT = {
-        "operator" : "-", \
-        "name" : "sub1",\
-        "priority" : 3, \
-        "arity" : 1, \
-        "actions" : "__neg__",\
-        "txt" :  "- {op1}",\
-        "tex" :  "- {op1}",\
+        "operator": "-",
+        "name": "sub1",
+        "priority": 3,
+        "arity": 1,
+        "actions": "__neg__",
+        "txt":  "- {op1}",
+        "tex":  "- {op1}",
         }
 
     def __init__(self):
diff --git a/pymath/calculus/test/test_expression.py b/pymath/calculus/test/test_expression.py
index cc34e0f..b9ebfe4 100644
--- a/pymath/calculus/test/test_expression.py
+++ b/pymath/calculus/test/test_expression.py
@@ -5,9 +5,6 @@
 
 
 from pymath.calculus.expression import Expression
-from pymath.calculus.fraction import Fraction
-from pymath.calculus.generic import first_elem
-from pymath.calculus.render import txt, tex
 from pymath.calculus.operator import op
 
 
diff --git a/pymath/calculus/test/test_render.py b/pymath/calculus/test/test_render.py
index 923366e..e8c40af 100644
--- a/pymath/calculus/test/test_render.py
+++ b/pymath/calculus/test/test_render.py
@@ -4,7 +4,7 @@
 
 import unittest
 
-from pymath.calculus.render import tex, txt, p2i
+from pymath.calculus.render import tex, txt
 from pymath.calculus.fraction import Fraction
 from pymath.calculus.polynom import Polynom
 from pymath.calculus.operator import op
diff --git a/pymath/calculus/test/test_str2tokens.py b/pymath/calculus/test/test_str2tokens.py
index 213bd2f..361f26a 100644
--- a/pymath/calculus/test/test_str2tokens.py
+++ b/pymath/calculus/test/test_str2tokens.py
@@ -57,7 +57,7 @@ class TestStr2tokens(unittest.TestCase):
         post = str2in_tokens(exp)
         self.assertEqual(post, [Polynom([0, 1]), "*", Polynom([0, 1]), '+', 4])
 
-    def test_str2tokens_poly(self):
+    def test_str2tokens_poly_par(self):
         exp = "x(2+1) + 4"
         post = str2in_tokens(exp)
         self.assertEqual(post, [Polynom([0, 1]), "*",