'Initiates an Express Checkout transaction.
Optionally, the SetExpressCheckout API operation can set up billing agreements for
reference transactions and recurring payments.
Returns a NVP instance - check for token and payerid to continue!'

def setExpressCheckout(self, params):

    if self._is_recurring(params):
        params = self._recurring_setExpressCheckout_adapter(params)
    defaults = {'method': 'SetExpressCheckout', 'noshipping': 1}
    required = L('returnurl    cancelurl    amt')
    return self._fetch(params, required, defaults)
