Deferred payment in Python for PayPal

paypal.py

import json
import requests

class PaymentInfo(object):
    def __init__(self, credit_card, transaction):
        self.credit_card = credit_card
        self.transaction = transaction

class CreditCard(object):
    def __init__(self, number, type, expire_month, expire_year, cvv2, first_name, last_name, billing_address):
        self.number = number
        self.type = type
        self.expire_month = expire_month
        self.expire_year = expire_year
        self.cvv2 = cvv2
        self.first_name = first_name
        self.last_name = last_name
        self.billing_address = billing_address

class InvalidCredentials(Exception):
    pass

class PayPal(object):
    def __init__(self, client_id, secret):
        self.client_id = client_id
        self.secret = secret

    def get_token(self):
        r = requests.post('https://api.sandbox.paypal.com/v1/oauth2/token', {
            'grant_type': 'client_credentials'
        }, auth=(self.client_id, self.secret))
        try:
            return r.json()['access_token']
        except (AttributeError,):
            raise InvalidCredentials()

    def authorize_payment(self, payment_info):
        """
        Authorizes a payment for up to 30 days.
        """
        if 'token' not in self.__dict__:
            self.token = self.get_token()
        data = json.dumps({
                          "intent": "authorize",
                          "payer": {
                              "payment_method": "credit_card",
                              "funding_instruments": [
                                  {"credit_card": payment_info.credit_card.__dict__}
                              ]
                          },
                          "transactions": [
                              {
                                  "amount": payment_info.transaction
                              }
                          ]
                      })
        r = requests.post("https://api.sandbox.paypal.com/v1/payments/payment",
                      data=data,
                      headers={
                          "Content-Type": "application/json",
                          "Authorization": "Bearer %s" % self.token
                      })

        if (r.status_code >= 400):
            print r.json()
        res = r.json()['transactions'][0]['related_resources'][0]
        # Not sure if we can guarantee the order here?
        capture_url = [x['href'] for x in res['authorization']['links'] if x['rel'] == 'capture'][0]
        auth_id = res['authorization']['id']

        return auth_id, capture_url


    def capture_payment(self, authorize_id, currency, total):
        """
        Captures (eg cashes) an already authorized payment
        """
        if 'token' not in self.__dict__:
            self.token = self.get_token()
        url = "https://api.sandbox.paypal.com/v1/payments/authorization/%s/capture" % authorize_id
        r = requests.post(url,
                          data=json.dumps({
                              "amount": {
                                  "currency": currency,
                                  "total": total,
                              },
                              "is_final_capture": "true",
                          }),
                          headers={"Authorization": "Bearer %s" % self.token})

        # TODO check status code