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msgspec.json.decode fails with KeyError when decoding dataclasses on Python 3.14 #876
Description
Description
Description:
When using Python 3.14, decoding a simple dataclass with msgspec.json.decode raises a KeyError. This occurs even with a minimal example.
Reproduction:
Save the following as main.py and run with: uv run main.py
# /// script
# requires-python = ">=3.14"
# dependencies = [
# "msgspec",
# ]
# ///
from dataclasses import dataclass
import msgspec.json
@dataclass
class Dummy:
field: str = "value"
c = Dummy()
msg = msgspec.json.encode(c)
msgspec.json.decode(msg, strict=True, type=Dummy)Error Message:
Traceback (most recent call last):
File "/xxxx/main.py", line 13, in <module>
msgspec.json.decode(msg, strict=True, type=Dummy)
File "/xxxx/.venv/lib/python3.14/site-packages/msgspec/_utils.py", line 254, in get_dataclass_info
typ = hints[name]
~~~~~^^^^^^
KeyError: 'field'
Expected behavior:
msgspec.json.decode should successfully decode the dataclass instance, matching behavior on Python 3.13 and earlier versions.
Additional context:
This seems to stem from msgspec._utils.get_class_annotations, which returns an empty dict under Python 3.14:
import msgspec._utils as utils
assert utils.get_class_annotations(Dummy) == {}Environment:
- Python: 3.14.0
- msgspec: 0.19.0
- Installed via: uv
- OS: Linux
Activity
mbsantiago commentedon Oct 13, 2025
I’m sorry, I just noticed that an existing PR (#852 ) already addresses this issue.
I tested my minimal reproduction against that branch and can confirm that the proposed fix resolves the problem.
I’ll leave this issue open for now since the PR hasn’t been merged yet — but once it is, this should be fully resolved.
return42 commentedon Oct 17, 2025
Duplicate of #651
I think its better when you add your review to #852
ofek commentedon Oct 19, 2025
Resolved by #852
ofek commentedon Nov 24, 2025
https://github.com/jcrist/msgspec/releases/tag/0.20.0