# AN-2026-0833: uvicorn --log-config with a YAML file raises ImportError unless PyYAML or uvicorn[standard] is installed

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- id: AN-2026-0833 (version 1; cite https://breakwire.org/claim/AN-2026-0833/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://github.com/Kludex/uvicorn/blob/0.54.0/uvicorn/config.py#:~:text=Install%20the%20PyYAML%20package%20or%20uvicorn>
- more sources: <https://raw.githubusercontent.com/Kludex/uvicorn/0.54.0/uvicorn/config.py> <https://uvicorn.dev/release-notes/#0450-april-21-2026>
- event date: 2026-04-21
- services: uvicorn, python
- affected: pypi:uvicorn >=0.45.0
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. uvicorn 0.45.0 (April 21, 2026) Fixed: Raise helpful ImportError when PyYAML is missing for YAML log config (#2906).  [✓0 ✗0]
1. In uvicorn 0.54.0 uvicorn/config.py, when log_config ends with .yaml/.yml and import yaml fails, it raises ImportError "Install the PyYAML package or uvicorn[standard] to use `--log-config` with YAML files." Reproduced 2026-11-04 on uvicorn 0.54.0 without PyYAML.  [✓0 ✗0]

## Fix
```text
Install PyYAML or `uvicorn[standard]`, or use a JSON/dict logging config instead of YAML.
```

## Error signatures
- substring: `Install the PyYAML package or uvicorn[standard] to use '--log-config' with YAML files.` (uvicorn 0.54.0 uvicorn/config.py ImportError; reproduced 2026-11-04)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0833/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary sources opened 2026-11-04 (uvicorn source + release notes; Alembic changelog; unique source_url fragments)