Ejemplo de codeo de descarga de factura en txt, en modulo account.invoice

file.txt

#ANADIDOS EN .PY CON EL FIN DE INGRESAR LOS CAMPOS A LA BD###
#############################################################
class InvoiceMaryun(models.Model):
    _inherit = 'account.invoice'

    txt_filename = fields.Char()
    txt_binary = fields.Binary()

    @api.one
    def generate_file(self):
        """
        function called from button
        """
        content = ''
        # make something to generate content
        return self.write({
            'txt_filename': 'file.txt',
            'txt_binary': base64.encodestring(content)
        })
        
#ANADIDOS EN VISTA XML CON EL FIN DE MOSTRAR EL BOTON DE DESCARGA###
####################################################################       
<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>
        <!-- Definimos la accion --> 

        <record model="ir.ui.view" id="account_invoice_maryun_inherit">
                <field name="name">account.invoice.maryun.inherit</field>
                <field name="model">account.invoice</field>
                <field name="type">form</field>
                <field name="inherit_id" ref="account.invoice_form"/>
                <field name="arch" type="xml">
                    <xpath expr="//notebook[last()]" position="inside">
                        <page string="Facturacion TXT" name="geo_localization">
                            <group colspan="2" col="2">
                                <separator string="Facturacion TXT" colspan="2"/>
                                <button name="generate_file" type="object" string="Generar Factura TXT"/>
                                <field name="txt_filename" invisible="1"/>
                            <field name="txt_binary" filename="txt_filename" readonly="1" string="Descarga el archivo"/>
                            </group>
                        </page>
                    </xpath>
                    <!-- <field name="invoice_line" position="after">
                            <button name="generate_file" type="object" string="Generar Factura TXT"/>
                            <field name="txt_filename" invisible="1"/>
                            <field name="txt_binary" filename="txt_filename" readonly="1"/>
                    </field> --> 
                </field>
        </record>
 
    </data>
</openerp>