Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

`http.client.HTTPSConnection._tunnel` raises `AttributeError: 'NoneType' object has no attribute 'encode'` when header value is `None`

Open Beginner friendly
  • Is something wrong?
#159,044 4 comments 0 reactions 0 assignees View on GitHub

Maintainers usually reply within 1 day

Nobody has claimed this yet.

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
68/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
python
Domain
backend, networking

Research direction

Start by reading http.client.HTTPSConnection._tunnel and the set_tunnel handling in Lib/http/client.py; compare the behavior with the 3.10.20 version identified in the report. Check existing tunnel tests in Lib/test/test_httplib.py and add coverage for a header value of None. Done means the regression is covered and _tunnel() no longer crashes for that input.

Written by the indexing model from the issue text.

Description

stdlib type-bug
Bug report
Bug Description

Calling http.client.HTTPSConnection._tunnel() raises AttributeError: 'NoneType' object has no attribute 'encode' when _tunnel_headers contains a header key with a None value.

This regression affects third-party libraries (such as Apache Thrift and CodeChecker) that pass header dictionaries containing None values into set_tunnel(..., headers=...) or HTTP connection objects.

In Python 3.10.21, _tunnel() introduced strict encoding of tunnel headers (value.encode("latin-1")) without checking if the header value is None.

Target Python Version

Python 3.10.21 (Regression introduced between 3.10.20 and 3.10.21)

Operating System

Linux / Ubuntu

Code to Reproduce
import http.client

conn = http.client.HTTPSConnection("127.0.0.1", 8080)

# Set tunnel with a header value of None
conn.set_tunnel("example.com", 443, headers={"X-Test-Header": None})

# Call _tunnel() to trigger the issue
conn._tunnel()
Expected Behavior

_tunnel() should gracefully handle or filter out header keys with None values (or handle string conversions) rather than crashing with an AttributeError.

Actual Behavior

Traceback (most recent call last):
File "reproduce.py", line 9, in
conn._tunnel()
File "/usr/lib/python3.10/http/client.py", line 936, in _tunnel
value_bytes = value.encode("latin-1")
AttributeError: 'NoneType' object has no attribute 'encode'

CPython versions tested on:

3.10

Operating systems tested on:

Linux

Dominant language
Python
Stars
77.6k
Forks
37.6k
Avg merge
1d 10h
Merged PRs (30d)
573

Getting set up

Open in Codespaces

Starts the project's dev container in your browser, under your own GitHub account.

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from python/cpython

All issues in python/cpython

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.