'Start an Express checkout.
You\'ll want to use this in conjunction with
:meth:`generate_express_checkout_redirect_url` to create a payment,
then figure out where to redirect the user to for them to
authorize the payment on PayPal\'s website.
Required Kwargs
* PAYMENTREQUEST_0_AMT
* PAYMENTREQUEST_0_PAYMENTACTION
* RETURNURL
* CANCELURL'

def set_express_checkout(self, **kwargs):

    return self._call('SetExpressCheckout', **kwargs)
