This is my code---

I want to visible this button based on payment method(journal_id) from Supplier Payment like If it is a Cash then ,this button should visible,otherwise(if its a bank not visible this button ),How Its Possible,need a help...

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from osv import osv,fields
from openerp.tools.translate import _

class customer_payments(osv.osv):
    _inherit='account.voucher'

    def _amount_all(self, cr, uid, ids, name, args, context=None):
        res = {}
        for invoice in self.browse(cr, uid, ids, context=context):
            res[invoice.id] = {
                'amount_total': 0.0
            }
            for line in invoice.line_dr_ids:
                res[invoice.id]['amount_total'] += line.amount
        return res

def cash_payment_popup(self, cr, uid, ids, context=None):

        if not ids: return []
        dummy, view_id = self.pool.get('ir.model.data').get_object_reference(cr, uid,'customer_payments', 'customer_payment_wizard_form_view')
        
        inv = self.browse(cr, uid, ids[0], context=context)
        return {
            'name':_("Customer Payments"),
            'view_mode': 'form',
            'view_id': view_id,
            'view_type': 'form',
            'res_model': 'customer.payment.wizard',
            'type': 'ir.actions.act_window',
            'nodestroy': True,
            'target': 'new',
            'domain': '[]',
            'context': {
                'default_supplier_name': self.pool.get('res.partner')._find_accounting_partner(inv.partner_id).id,
                'default_amount': inv.amount_total,
                'default_date': inv.date,
             #   'default_currency': self.pool.get('account.invoice')._get_currency(inv.currency_id).id,
             #   'default_company_name': self.pool.get('res.partner')._find_accounting_partner(inv.company_id).id,
                'default_cash_payment_order_no':inv.reference,
                'default_document': inv.document,
                'default_date_location': inv.date_location,
                'default_purpose': inv.purpose,
                'default_enclosure': inv.enclosure,
           #     'default_amount_words':inv.amount_words,
           #     'default_accounts':inv.ren_period,
                        }
        }

customer_payments()

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<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
            <record id="supplier_payment_inherited" model="ir.ui.view">
                <field name="name">supplier.payment.view.form</field>
                <field name="model">account.voucher</field>
                <field name="type">form</field>
                <field name="inherit_id" ref="account_voucher.view_vendor_payment_form"/>
                <field name="arch" type="xml">
            <xpath expr="/form/sheet/field[3]" position="after">
    <button name="cash_payment_popup" string="Cash Payment Order" type="object" class="oe_right oe_highlight"/>
            </xpath>
                    <xpath expr="/form/sheet/group/group[1]/field[4]" position="after">
                        <field name="date_location"/>
                        <field name="enclosure"/>
                    </xpath>
                    <xpath expr="/form/sheet/group/group[2]/field[4]" position="after">
                        <field name="document"/>
                        <field name="purpose"/>
                    </xpath>
                </field>
            </record>
                                                        
    </data>
</openerp>