Запросы на Python: как настроить формат `request payload` формата HTML в запросе POST? [Дубликат]

Просто отправьте xml байты напрямую:

#!/usr/bin/env python2
# -*- coding: utf-8 -*-
import requests

xml = """<?xml version='1.0' encoding='utf-8'?>
<a>б</a>"""
headers = {'Content-Type': 'application/xml'} # set what your server accepts
print requests.post('http://httpbin.org/post', data=xml, headers=headers).text

Выход

{
  "origin": "x.x.x.x",
  "files": {},
  "form": {},
  "url": "http://httpbin.org/post",
  "args": {},
  "headers": {
    "Content-Length": "48",
    "Accept-Encoding": "identity, deflate, compress, gzip",
    "Connection": "keep-alive",
    "Accept": "*/*",
    "User-Agent": "python-requests/0.13.9 CPython/2.7.3 Linux/3.2.0-30-generic",
    "Host": "httpbin.org",
    "Content-Type": "application/xml"
  },
  "json": null,
  "data": "<?xml version='1.0' encoding='utf-8'?>\n<a>\u0431</a>"
}