Python Requests: Invalid Header Name

Question

I am trying to send a request with the header: ":hello". However, the leading colon causes the script to not function properly, and emit this traceback:

Traceback (most recent call last):

(first few lines removed for my privacy)

File "C:\Python27\lib\site-packages\requests\api.py", line 109, in post
    return request('post', url, data=data, json=json, **kwargs)
  File "C:\Python27\lib\site-packages\requests\api.py", line 50, in request
    response = session.request(method=method, url=url, **kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 468, in request
    resp = self.send(prep, **send_kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 576, in send
    r = adapter.send(request, **kwargs)
  File "C:\Python27\lib\site-packages\requests\adapters.py", line 370, in send
    timeout=timeout
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 559, in urlopen
    body=body, headers=headers)
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 353, in _make_request
    conn.request(method, url, **httplib_request_kw)
  File "C:\Python27\lib\httplib.py", line 1057, in request
    self._send_request(method, url, body, headers)
  File "C:\Python27\lib\httplib.py", line 1096, in _send_request
    self.putheader(hdr, value)
  File "C:\Python27\lib\httplib.py", line 1030, in putheader
    raise ValueError('Invalid header name %r' % (header,))
ValueError: Invalid header name ':hello'

Is there a workaround for this? My script is:

import requests
headers = {'user-agent': 'alsotesting', ':hello': 'test'}
requests.post("my server", headers=headers)

Answer 1

As your error says, :header is not a valid HTTP header name (you cannot start headers with ":" - see documentation). You should change

headers = {'user-agent': 'alsotesting', ':hello': 'test'}

to

headers = {'user-agent': 'alsotesting', 'hello': 'test'}

Edit: HTTP/2 uses pseudo-headers fields, which start with a colon (see documentation). Also, as explained here, you may see some headers starting with a colon in Chrome's Developer Tools, which can happen when Chrome is talking to a web server using SPDY - and also HTTP/2 (which is based on SPDY/2), which correspond to pseudo-headers. As stated in documentation, pseudo-header fields are not HTTP header fields.

In conclusion, header fields starting with a colon are not allowed with standard HTTP protocol, so that is why you are getting the Invalid header name error