diff --git a/bin/ir/ir.py b/bin/ir/ir.py
index 109faf95872..c4cc435765d 100644
--- a/bin/ir/ir.py
+++ b/bin/ir/ir.py
@@ -31,7 +31,7 @@ def ir_del(cr, uid, id):
     obj = pooler.get_pool(cr.dbname).get('ir.values')
     return obj.unlink(cr, uid, [id])
 
-def ir_get(cr, uid, key, key2, models, meta=False, context={}, res_id_req=False):
+def ir_get(cr, uid, key, key2, models, meta=False, context=None, res_id_req=False):
     obj = pooler.get_pool(cr.dbname).get('ir.values')
     res = obj.get(cr, uid, key, key2, models, meta=meta, context=context, res_id_req=res_id_req)
     return res
diff --git a/bin/osv/fields.py b/bin/osv/fields.py
index c043f7a30e7..a5839381f27 100644
--- a/bin/osv/fields.py
+++ b/bin/osv/fields.py
@@ -63,8 +63,10 @@ class _column(object):
     _symbol_set = (_symbol_c, _symbol_f)
     _symbol_get = None
 
-    def __init__(self, string='unknown', required=False, readonly=False, domain=None, context={}, states=None, priority=0, change_default=False, size=None, ondelete="set null", translate=False, select=False, **args):
-        if not context:
+    def __init__(self, string='unknown', required=False, readonly=False, domain=None, context=None, states=None, priority=0, change_default=False, size=None, ondelete="set null", translate=False, select=False, **args):
+        if domain is None:
+            domain = []
+        if context is None:
             context = {}
         self.states = states or {}
         self.string = string
@@ -76,7 +78,7 @@ class _column(object):
         self.change_default = change_default
         self.ondelete = ondelete
         self.translate = translate
-        self._domain = domain or []
+        self._domain = domain
         self._context = context
         self.write = False
         self.read = False
@@ -403,7 +405,7 @@ class one2many(_column):
         assert(self.change_default != True)
 
     def get_memory(self, cr, obj, ids, name, user=None, offset=0, context=None, values=None):
-        if not context:
+        if context is None:
             context = {}
         if self._context:
             context = context.copy()
@@ -786,7 +788,7 @@ class function(_column):
 
 class related(function):
 
-    def _fnct_search(self, tobj, cr, uid, obj=None, name=None, domain=None, context={}):
+    def _fnct_search(self, tobj, cr, uid, obj=None, name=None, domain=None, context=None):
         self._field_get2(cr, uid, obj, context)
         i = len(self._arg)-1
         sarg = name
@@ -803,7 +805,7 @@ class related(function):
         return [(self._arg[0], 'in', sarg)]
 
     def _fnct_write(self,obj,cr, uid, ids, field_name, values, args, context=None):
-        self._field_get2(cr, uid, obj, context)
+        self._field_get2(cr, uid, obj, context=context)
         if type(ids) != type([]):
             ids=[ids]
         objlst = obj.browse(cr, uid, ids)
@@ -884,7 +886,7 @@ class related(function):
             # TODO: improve here to change self.store = {...} according to related objects
             pass
 
-    def _field_get2(self, cr, uid, obj, context={}):
+    def _field_get2(self, cr, uid, obj, context=None):
         if self._relations:
             return
         obj_name = obj._name
@@ -904,10 +906,10 @@ class related(function):
 # ---------------------------------------------------------
 
 class dummy(function):
-    def _fnct_search(self, tobj, cr, uid, obj=None, name=None, domain=None, context={}):
+    def _fnct_search(self, tobj, cr, uid, obj=None, name=None, domain=None, context=None):
         return []
 
-    def _fnct_write(self,obj,cr, uid, ids, field_name, values, args, context=None):
+    def _fnct_write(self, obj, cr, uid, ids, field_name, values, args, context=None):
         return False
 
     def _fnct_read(self, obj, cr, uid, ids, field_name, args, context=None):
diff --git a/bin/osv/orm.py b/bin/osv/orm.py
index bac069847bc..d4c66683999 100644
--- a/bin/osv/orm.py
+++ b/bin/osv/orm.py
@@ -126,12 +126,14 @@ class browse_record_list(list):
 class browse_record(object):
     logger = netsvc.Logger()
 
-    def __init__(self, cr, uid, id, table, cache, context=None, list_class = None, fields_process={}):
+    def __init__(self, cr, uid, id, table, cache, context=None, list_class=None, fields_process=None):
         '''
         table : the object (inherited from orm)
         context : dictionary with an optional context
         '''
-        if not context:
+        if fields_process is None:
+            fields_process = {}
+        if context is None:
             context = {}
         self._list_class = list_class or browse_record_list
         self._cr = cr
@@ -404,7 +406,9 @@ class orm_template(object):
     def read_group(self, cr, uid, domain, fields, groupby, offset=0, limit=None, context=None):
         raise NotImplementedError(_('The read_group method is not implemented on this object !'))
 
-    def _field_create(self, cr, context={}):
+    def _field_create(self, cr, context=None):
+        if context is None:
+            context = {}
         cr.execute("SELECT id FROM ir_model WHERE model=%s", (self._name,))
         if not cr.rowcount:
             cr.execute('SELECT nextval(%s)', ('ir_model_id_seq',))
@@ -489,8 +493,8 @@ class orm_template(object):
                         break
         cr.commit()
 
-    def _auto_init(self, cr, context={}):
-        self._field_create(cr, context)
+    def _auto_init(self, cr, context=None):
+        self._field_create(cr, context=context)
 
     def __init__(self, cr):
         if not self._name and not hasattr(self, '_inherit'):
@@ -506,7 +510,7 @@ class orm_template(object):
         if not self._table:
             self._table = self._name.replace('.', '_')
 
-    def browse(self, cr, uid, select, context=None, list_class=None, fields_process={}):
+    def browse(self, cr, uid, select, context=None, list_class=None, fields_process=None):
         """
         Fetch records as objects allowing to use dot notation to browse fields and relations
 
@@ -517,8 +521,6 @@ class orm_template(object):
         :rtype: object or list of objects requested
 
         """
-        if not context:
-            context = {}
         self._list_class = list_class or browse_record_list
         cache = {}
         # need to accepts ints and longs because ids coming from a method
@@ -526,7 +528,7 @@ class orm_template(object):
         if isinstance(select, (int, long)):
             return browse_record(cr, uid, select, self, cache, context=context, list_class=self._list_class, fields_process=fields_process)
         elif isinstance(select, list):
-            return self._list_class([browse_record(cr, uid, id, self, cache, context=context, list_class=self._list_class, fields_process=fields_process) for id in select], context)
+            return self._list_class([browse_record(cr, uid, id, self, cache, context=context, list_class=self._list_class, fields_process=fields_process) for id in select], context=context)
         else:
             return browse_null()
 
@@ -1498,14 +1500,14 @@ class orm_template(object):
 
         return arch
 
-    def __get_default_search_view(self, cr, uid, context={}):
+    def __get_default_search_view(self, cr, uid, context=None):
 
         def encode(s):
             if isinstance(s, unicode):
                 return s.encode('utf8')
             return s
 
-        view = self.fields_view_get(cr, uid, False, 'form', context)
+        view = self.fields_view_get(cr, uid, False, 'form', context=context)
 
         root = etree.fromstring(encode(view['arch']))
         res = etree.XML("""<search string="%s"></search>""" % root.get("string", ""))
@@ -2410,7 +2412,9 @@ class orm(orm_template):
                 self.__schema.debug("Table '%s': column '%s': dropped NOT NULL constraint",
                                     self._table, column['attname'])
 
-    def _auto_init(self, cr, context={}):
+    def _auto_init(self, cr, context=None):
+        if context is None:
+            context = {}
         store_compute = False
         create = False
         todo_end = []
diff --git a/bin/tools/convert.py b/bin/tools/convert.py
index a69885be4db..14823984ca3 100644
--- a/bin/tools/convert.py
+++ b/bin/tools/convert.py
@@ -655,7 +655,7 @@ 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 19cf1db68cb..7d9bf3af700 100644
--- a/bin/tools/pdf_utils.py
+++ b/bin/tools/pdf_utils.py
@@ -60,7 +60,7 @@ trailer
 %%EOF
 """
 
-def output_field( f ):
+def output_field(f):
     return "\xfe\xff" + "".join( [ "\x00"+c for c in f ] )
 
 def extract_keys(lines):