from gluon import XML

def button(merchant_id="123456789012345",
           products=[dict(name="shoes",
                          quantity=1,
                          price=23.5,
                          currency='USD',
                          description="running shoes black")]):
    t = '<input name="item_%(key)s_%(k)s" type="hidden" value="%(value)s"/>\n'
    list_products = ''
    for k, product in enumerate(products):
        for key in ('name','description','quantity','price','currency'):
            list_products += t % dict(k=k + 1, key=key, value=product[key])
    button = """<form action="https://checkout.google.com/api/checkout/v2/checkoutForm/Merchant/%(merchant_id)s" id="BB_BuyButtonForm" method="post" name="BB_BuyButtonForm" target="_top">\n%(list_products)s<input name="_charset_" type="hidden" value="utf-8"/>\n<input alt="" src="https://checkout.google.com/buttons/buy.gif?merchant_id=%(merchant_id)s&amp;w=117&amp;h=48&amp;style=white&amp;variant=text&amp;loc=en_US" type="image"/>\n</form>""" % dict(merchant_id=merchant_id, list_products=list_products)
    return XML(button)