PayPal的Python接口-urllib.urlencode非ASCII字符失败

我正在尝试实现PayPal IPN功能。基本协议如下:

1. 客户将从我的网站重定向到PayPal的网站以完成付款。他登录自己的账户,授权付款。
2. PayPal调用我服务器上的一个页面,以POST方式传递详细信息。详细信息包括一个人的姓名、地址和付款信息等。

While calling send_response_to_paypal. Traceback (most recent call last):
  File "<snip>/account/paypal/views.py", line 108, in process_paypal_ipn
    verify_result = send_response_to_paypal(params)
  File "<snip>/account/paypal/views.py", line 41, in send_response_to_paypal
    params = urllib.urlencode(params)
  File "/usr/local/lib/python2.6/urllib.py", line 1261, in urlencode
    v = quote_plus(str(v))
UnicodeEncodeError: 'ascii' codec can't encode character u'\ufffd' in position 9: ordinal not in range(128)

据我所知,urlencode采用ASCII编码,在某些情况下,用户的联系信息可能包含非ASCII字符。这是可以理解的。我的问题是,如何使用urllib2.urlopen(req)(或其他方法)对非ASCII字符进行编码,以便将POSTing发送到URL

我阅读了PayPal原始请求中的参数如下(GET用于测试):

def read_ipn_params(request):
    if request.POST:  
        params= request.POST.copy()  
        if "ipn_auth" in request.GET:
            params["ipn_auth"]=request.GET["ipn_auth"]
        return params
    else:  
        return request.GET.copy()  

def send_response_to_paypal(params):
    params['cmd']='_notify-validate'  
    params = urllib.urlencode(params)  
    req = urllib2.Request(PAYPAL_API_WEBSITE, params)  
    req.add_header("Content-type", "application/x-www-form-urlencoded") 
    response = urllib2.urlopen(req)  
    status = response.read()  
    if not status == "VERIFIED":  
        logging.warn("PayPal cannot verify IPN responses: " + status)
        return False

    return True

显然,只有当某人的姓名或地址或用于PayPal支付的其他字段不在ASCII范围内时,才会出现问题。