Posting a mutlipart-encoded file with non-ASCII characters in filename doesn't work

The following code doesn’t actually upload any data to the server:

r = requests.post('https://gs.smuglo.li/api/statusnet/media/upload',
    auth=('testbot', 'testbot'),
    files={'media': open('/tmp/Снимок экрана_2016-07-27_05-15-38.png', 'rb')})

[ghost]

@Lukasa Is this Python 2? Because in Python 3 I get

TypeError: a bytes-like object is required, not 'str'

[ghost]

@Lukasa Sure

>>> filename = '/tmp/Снимок экрана_2016-07-27_05-15-38.png' 
>>> media = {'media':(filename.encode('utf-8'), open(filename, 'rb'))}
>>> r = requests.post(url, auth=('testbot', 'testbot'), files=media)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
    r = requests.post(url, auth=(username, password), files=media)
  File "/usr/lib/python3.5/site-packages/requests/api.py", line 111, in post
    return request('post', url, data=data, json=json, **kwargs)
  File "/usr/lib/python3.5/site-packages/requests/api.py", line 57, in request
    return session.request(method=method, url=url, **kwargs)
  File "/usr/lib/python3.5/site-packages/requests/sessions.py", line 461, in request
    prep = self.prepare_request(req)
  File "/usr/lib/python3.5/site-packages/requests/sessions.py", line 394, in prepare_request
    hooks=merge_hooks(request.hooks, self.hooks),
  File "/usr/lib/python3.5/site-packages/requests/models.py", line 298, in prepare
    self.prepare_body(data, files, json)
  File "/usr/lib/python3.5/site-packages/requests/models.py", line 449, in prepare_body
    (body, content_type) = self._encode_files(files, data)
  File "/usr/lib/python3.5/site-packages/requests/models.py", line 155, in _encode_files
    rf.make_multipart(content_type=ft)
  File "/usr/lib/python3.5/site-packages/urllib3/fields.py", line 174, in make_multipart
    (('name', self._name), ('filename', self._filename))
  File "/usr/lib/python3.5/site-packages/urllib3/fields.py", line 134, in _render_parts
    parts.append(self._render_part(name, value))
  File "/usr/lib/python3.5/site-packages/urllib3/fields.py", line 114, in _render_part
    return format_header_param(name, value)
  File "/usr/lib/python3.5/site-packages/urllib3/fields.py", line 35, in format_header_param
    if not any(ch in value for ch in '"\\\r\n'):
  File "/usr/lib/python3.5/site-packages/urllib3/fields.py", line 35, in <genexpr>
    if not any(ch in value for ch in '"\\\r\n'):
TypeError: a bytes-like object is required, not 'str'