Create a new method on statement lines to get the currency

account_statement_operation_rule/model/account_statement_line.py

@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+##############################################################################
+#
+#    Author: Guewen Baconnier
+#    Copyright 2014 Camptocamp SA
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU Affero General Public License as
+#    published by the Free Software Foundation, either version 3 of the
+#    License, or (at your option) any later version.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU Affero General Public License for more details.
+#
+#    You should have received a copy of the GNU Affero General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+##############################################################################
+
+
+from openerp import models, api
+
+
+class AccountBankStatementLine(models.Model):
+    _inherit = 'account.bank.statement.line'
+
+    @api.multi
+    def currency_for_rules(self):
+        return self.currency_id or self.statement_id.currency