Python封装multipart/form-data格式表单数据代码片段

multipart/form-data类型的POST实体结构相对来说（常规的POST正文采用application/x-www-form-urlencoded格式）比较复杂，它常用于文件上传。
下面是一个multipart/form-data格式的POST实体示例

-----------------------------114782935826962  
Content-Disposition: form-data; name="dv_deputy"  
  
e5471d92ebec3654ee6b90d131d296f4  
-----------------------------114782935826962  
Content-Disposition: form-data; name="form_id"  
  
submit_new_resume  
-----------------------------114782935826962  
Content-Disposition: form-data; name="resumator-subdomain-value"  
  
app  
-----------------------------114782935826962  
Content-Disposition: form-data; name="resumator-tags-value"  
  
  
-----------------------------114782935826962  
Content-Disposition: form-data; name="resumator-job-value"  
  
0  
-----------------------------114782935826962  
Content-Disposition: form-data; name="manual"  
  
true  
  
-----------------------------114782935826962  
Content-Disposition: form-data; name="resumator-eeo_disability-value"  
  
0  
-----------------------------114782935826962--  
最后这里还有一个空行  

封装代码如下：

# coding: utf-8  
# util.py  
  
import os  
import mimetypes  
import mimetools  
  
def get_content_type(filepath):  
    return mimetypes.guess_type(filepath)[0] or 'application/octet-stream'  
  
def encode_multipart_formdata(fields, files=[]):  
    """ 
    fields is a sequence of (name, value) elements for regular form fields. 
    files is a sequence of (name, filepath) elements for data to be uploaded as files 
    Return (content_type, body) ready for httplib.HTTP instance 
    """  
    BOUNDARY = mimetools.choose_boundary()  
    CRLF = '\r\n'  
    L = []  
    for (key, value) in fields:  
        L.append('--' + BOUNDARY)  
        L.append('Content-Disposition: form-data; name="%s"' % key)  
        L.append('')  
        L.append(value)  
    for (key, filepath) in files:  
        L.append('--' + BOUNDARY)  
        L.append('Content-Disposition: form-data; name="%s"; filename="%s"' % (key, os.path.basename(filepath)))  
        L.append('Content-Type: %s' % get_content_type(filepath))  
        L.append('')  
        L.append(open(filepath, 'rb').read())  
    L.append('--' + BOUNDARY + '--')  
    L.append('')  
    body = CRLF.join(L)  
    content_type = 'multipart/form-data; boundary=%s' % BOUNDARY  
    return content_type, body  

encode_multipart_formdata返回的content_type应设置为content-type头。body即为封装后的数据。
参考：http://code.activestate.com/recipes/146306/