Bugfix Config.from_object on Config instances (closes #244)

[jbbqqf]

Summary

Config.from_object raises AttributeError: property 'cert_reqs' of 'Config' object has no getter when handed a populated Config() instance — i.e. when a user runs

hypercorn --config python:my_module.config app:app

with my_module.config = Config(); my_module.config.bind = "...". This is the documented use case in the from_object docstring.

Root cause: from_object iterates dir(instance) and calls getattr on every name, but cert_reqs is intentionally a write-only property (the deprecation alias for verify_mode). The getattr raises before the dict-comprehension can decide what to do.

Fix: skip names whose getter raises AttributeError. The deprecation alias is preserved (it still works when set via attribute write), but no longer crashes the loader.

Fixes #244.

Changes

• src/hypercorn/config.py — convert from_object's dict comprehension to a loop that swallows AttributeError; comment cites the issue.
• tests/test_config.py — test_config_from_object_accepts_config_instance round-trips a populated Config() and asserts the values survive.

Reproduce BEFORE/AFTER yourself (copy-paste)

# --- one-time setup ---
rm -rf /tmp/hc-244 && git clone https://github.com/pgjones/hypercorn.git /tmp/hc-244 && cd /tmp/hc-244
python3.11 -m venv .venv && source .venv/bin/activate
pip install -e . pytest pytest-asyncio pytest-trio trio httpx hypothesis mock

# --- BEFORE: origin/main, expect AttributeError ---
git checkout origin/main
python -c "
from hypercorn.config import Config
c = Config(); c.bind = '0.0.0.0:8080'
print(Config.from_object(c).bind)
"
# Expected: AttributeError: property 'cert_reqs' of 'Config' object has no getter

# --- AFTER: this branch, expect ['0.0.0.0:8080'] ---
git fetch https://github.com/jbbqqf/hypercorn.git fix/244-config-from-object-writeonly-property
git checkout FETCH_HEAD
python -c "
from hypercorn.config import Config
c = Config(); c.bind = '0.0.0.0:8080'
print(Config.from_object(c).bind)
"
# Expected: ['0.0.0.0:8080']

What I ran locally

$ pytest tests/test_config.py -v
========== 14 passed in 0.02s ==========

$ pytest -x --timeout=30 -q
197 passed in 6.29s

$ black --check src/hypercorn/config.py tests/test_config.py
2 files would be left unchanged.

$ isort --check src/hypercorn tests
(no output — clean)

$ flake8 src/hypercorn/ tests/
(no output — clean)

The new regression test fails on origin/main with the exact AttributeError cited in #244 and passes on the fix branch.

Edge cases

#	Scenario	Source	Expected	Verified by
1	Module-as-config (existing supported form)	from_object("module")	unchanged behaviour	test_config_from_object (existing)
2	Populated Config() instance (the bug)	c = Config(); c.bind = [...]; from_object(c)	round-trips	test_config_from_object_accepts_config_instance (new)
3	Plain object with mixed-readability properties	any class with @property write-only	property silently skipped	covered by (2) — cert_reqs is exactly this
4	Module attribute (ModuleType filter)	from_object(...) on a module that imports os	os skipped (unchanged)	preserved isinstance(value, ModuleType) check

Risk / blast radius

Single function, single behavioural change: previously-unreachable code paths now reach from_mapping. Nothing in the project's own test suite regressed (197 / 197). The only observable difference for existing users is that from_object now tolerates write-only properties — that cannot break a working caller.

---

PR drafted with assistance from Claude Code (Anthropic). The change was reviewed manually against hypercorn's source. The reproducer block above is the one I used during development; reviewers can paste it verbatim.

[TomiBelan]

This feels very unnecessarily complicated. Wouldn't it be easier and more reliable to just add this?

if isinstance(instance, cls):
    return instance

Note: I am a random passerby. My "request changes" is not official. You can decide to ignore it.