Python调用RESTful API时踩到的各类坑

开篇首先推荐一款REST接口调试的利器，Chrome的扩展程序Advanced REST client，功能十分齐全！使用它来模拟访问接口能够获取到详尽的信息，借助它排查接口是否可用。

问题1：curl访问API成功，可是使用python的urllib2模块访问却返回400。
接口规则以下：
POST /v2.0/tokens HTTP/1.0
Host: 192.168.85.183:35357
Content-Type: application/json
Accept: application/json
{
    "auth":{
        "passwordCredentials":{
            "username":"alan",
            "password":"admin"
        },
        "tenantName":"swifttenant1"
    }
}

cURL模拟访问实现以下：

curl -s -d '{"auth":{"passwordCredentials":{"username":"alan","password":"admin"},"tenantName":"swifttenant1"}}' -H "Content-type: application/json" http://192.168.85.183:35357/v2.0/tokens | python -mjson.tool

后台日志：
2013-09-03 05:34:20.133 23199 INFO access [-] 192.168.85.183 - - [03/Sep/2013:12:34:20 +0000] "POST http://192.168.85.183:35357/v2.0/tokens HTTP/1.0" 200 2711

python使用urllib2模块：

#!/usr/bin/python
import urllib
import urllib2

def curl_keystone_failed():
    url = 'http://192.168.85.183:35357/v2.0/tokens'
    values = {"auth":{"passwordCredentials":{"username":"alan","password":"admin"},"tenantName":"swifttenant1"}}
    # 这里千万不要仿照网上的方法进行加密，由于它自己就没有加密的一个过程！否则仍是会返回400的！
    # params = urllib.urlencode(values)
    params = str(values)
    headers = {"Content-type":"application/json","Accept": "application/json"}
    req = urllib2.Request(url, params, headers)
    response = urllib2.urlopen(req)
    print response.read()

if __name__ == "__main__":
    curl_keystone_failed()

后台日志：
2013-09-03 05:43:11.928 23199 INFO access [-] 192.168.85.185 - - [03/Sep/2013:12:43:11 +0000] "POST http://192.168.85.183:35357/v2.0/tokens HTTP/1.0" 400 244

随后使用httplib重写方法，查看返回的报错信息可发现，它没有获取到一个有效json格式的内容，原来python传输的时候是严格断定内容的type的。使用json来dumps一下能够解决问题！

def curl_keystone():
    url = 'http://192.168.85.183:35357/v2.0/tokens'
    values = {"auth":{"passwordCredentials":{"username":"alan","password":"admin"},"tenantName":"swifttenant1"}}
    params = json.dumps(values)
    headers = {"Content-type":"application/json","Accept": "application/json"}
    req = urllib2.Request(url, params, headers)
    response = urllib2.urlopen(req)
    print response.read()

后台日志： 
2013-09-03 05:50:52.884 23199 INFO access [-] 192.168.85.185 - - [03/Sep/2013:12:50:52 +0000] "POST http://192.168.85.183:35357/v2.0/tokens HTTP/1.0" 200 2711