Sample code for "multiple message-header fields with the same field-name" in Python plus requests

MultiValueHeaders.py

from collections import OrderedDict
from http.client import HTTPMessage


class MultiValueHeaders(HTTPMessage):
    '''https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2'''
    _separator_ = ', '
    def items(self):
        headers = OrderedDict()
        for key, value in super().items():
            headers.setdefault(key, []).append(value)
        return [(key, self._separator_.join(headers[key])) for key in headers]


import requests


headers = MultiValueHeaders()
headers.add_header('x-test', 'v1')
headers.add_header('x-test', 'v2')
with requests.get('http://localhost:8000/', headers=headers):
    pass