diff --git a/account_chart_update/wizard/wizard_chart_update.py b/account_chart_update/wizard/wizard_chart_update.py
index b0b6d31d1..57bb20fac 100644
--- a/account_chart_update/wizard/wizard_chart_update.py
+++ b/account_chart_update/wizard/wizard_chart_update.py
@@ -82,7 +82,7 @@ class WizardLog:
 class wizard_update_charts_accounts(orm.TransientModel):
     _name = 'wizard.update.charts.accounts'
 
-    def _get_lang_selection_options(self, cr, uid, context={}):
+    def _get_lang_selection_options(self, cr, uid, context=None):
         """
         Gets the available languages for the selection.
         """
diff --git a/account_credit_control/policy.py b/account_credit_control/policy.py
index 53214a838..0b4a5c8ca 100644
--- a/account_credit_control/policy.py
+++ b/account_credit_control/policy.py
@@ -336,8 +336,8 @@ class CreditControlPolicyLevel(orm.Model):
     # ----- sql time related methods ---------
 
     def _net_days_get_boundary(self):
-        return " (mv_line.date_maturity + %(delay)s)::date <= "
-        "date(%(controlling_date)s)"
+        return (" (mv_line.date_maturity + %(delay)s)::date <= "
+                "date(%(controlling_date)s)")
 
     def _end_of_month_get_boundary(self):
         return ("(date_trunc('MONTH', (mv_line.date_maturity + %(delay)s))+"
diff --git a/currency_rate_update/company.py b/currency_rate_update/company.py
index 606a15f50..5a3bc4c74 100644
--- a/currency_rate_update/company.py
+++ b/currency_rate_update/company.py
@@ -24,7 +24,7 @@ from openerp.osv import fields, orm
 class res_company(orm.Model):
     """override company to add currency update"""
 
-    def _multi_curr_enable(self, cr, uid, ids, field_name, arg, context={}):
+    def _multi_curr_enable(self, cr, uid, ids, field_name, arg, context=None):
         "check if multi company currency is enabled"
         result = {}
         fields = self.pool.get('ir.model.fields').search(
diff --git a/currency_rate_update/currency_rate_update.py b/currency_rate_update/currency_rate_update.py
index 6a32653cf..91419dfdc 100644
--- a/currency_rate_update/currency_rate_update.py
+++ b/currency_rate_update/currency_rate_update.py
@@ -177,7 +177,7 @@ class Currency_rate_update(osv.Model):
             cron_id = cron_obj.create(cr, uid, self.cron, context)
         return cron_id
 
-    def save_cron(self, cr, uid, datas, context={}):
+    def save_cron(self, cr, uid, datas, context=None):
         """save the cron config data should be a dict"""
         cron_id = self.get_cron_id(cr, uid, context)
         return self.pool.get('ir.cron').write(cr, uid, [cron_id], datas)