diff --git a/bin/tools/convert.py b/bin/tools/convert.py
index 973e762cd2e..20f54e15f11 100644
--- a/bin/tools/convert.py
+++ b/bin/tools/convert.py
@@ -598,7 +598,7 @@ form: module.record_id""" % (xml_id,)
             self.pool.get('ir.model.data').ir_set(cr, self.uid, 'action', 'tree_but_open', 'Menuitem', [('ir.ui.menu', int(pid))], action, True, True, xml_id=rec_id)
         return ('ir.ui.menu', pid)
 
-    def _assert_equals(self, f1, f2, prec = 4):
+    def _assert_equals(self, f1, f2, prec=4):
         return not round(f1 - f2, prec)
 
     def _tag_assert(self, cr, rec, data_node=None):
diff --git a/bin/tools/copy.py b/bin/tools/copy.py
index e6583dcfadf..badd4d51fc5 100644
--- a/bin/tools/copy.py
+++ b/bin/tools/copy.py
@@ -164,7 +164,7 @@ d[types.InstanceType] = _copy_inst
 
 del d
 
-def deepcopy(x, memo=None, _nil=[]):
+def deepcopy(x, memo=None, _nil=None):
     """Deep copy operation on arbitrary Python objects.
 
     See the module's __doc__ string for more info.
@@ -172,6 +172,8 @@ def deepcopy(x, memo=None, _nil=[]):
 
     if memo is None:
         memo = {}
+    if _nil is None:
+        _nil = {}
 
     d = id(x)
     y = memo.get(d, _nil)
diff --git a/bin/tools/pdf_utils.py b/bin/tools/pdf_utils.py
index 4782e544429..0286b9cf46d 100644
--- a/bin/tools/pdf_utils.py
+++ b/bin/tools/pdf_utils.py
@@ -58,7 +58,7 @@ trailer
 %%EOF
 """
 
-def output_field( f ):
+def output_field(f):
     return "\xfe\xff" + "".join( [ "\x00"+c for c in f ] )
 
 def extract_keys(lines):