Event Model

1.23.1 verified Fri May 01 auth: no python

Data model used by the bluesky ecosystem. Defines schemas for experimental data documents (e.g., Event, EventDescriptor, RunStart). Currently at version 1.23.1, released on a monthly cadence.

pip install event-model

Common errors

error ImportError: cannot import name 'Event' from 'event_model.schemas' ↓

cause Event is exported from the top-level event_model package, not from event_model.schemas.

fix

Use: from event_model import Event

error AttributeError: 'Event' object has no attribute 'dict' ↓

cause In v1.23, Event is a TypedDict, not a pydantic BaseModel. pydantic's .dict() is not available.

fix

Use: dict(event) or copy with dict(event)

error ValidationError: 1 validation error for DataKey precision none is not an allowed value (type=type_error.none.not_allowed) ↓

cause In v1.22.0+, DataKey fields like 'precision' cannot be None; omit the key if not needed.

fix

Remove the field or use a valid value.

Warnings

breaking In v1.23, the internal representation changed from pydantic BaseModel to jsonschema + TypedDict. Code that relied on pydantic methods (e.g., .dict(), .copy()) will break. Use dict() and copy from the TypedDict protocol instead. ↓

fix Replace .dict() with dict(doc) and .copy() with dict(doc); avoid pydantic-specific features.

breaking In v1.21, StreamResource and StreamDatum schemas changed significantly: `path_semantics` and `resource_kwargs` removed; `uri`, `parameters`, and `mimetype` added. ↓

fix Update code that creates StreamResource/StreamDatum to use new fields; drop old fields.

gotcha In v1.22.0, DataKey fields `precision`, `choices`, and `units` became required (non-optional). Leaving them out is still allowed, but providing None raises a validation error. ↓

fix Remove None values from those fields; omit the keys entirely if not needed.

Imports

Event
wrong
```
from event_model.schemas import Event
```
correct
```
from event_model import Event
```
Event is exported from the top-level package, not from submodules
RunStart
wrong
```
from bluesky_models import RunStart
```
correct
```
from event_model import RunStart
```
The correct package is event-model, not bluesky_models
EventDescriptor
wrong
```
from bluesky import event_model
```
correct
```
from event_model import EventDescriptor
```
bluesky package does not re-export event-model types directly

Quickstart

Create and print basic event-model documents

from event_model import Event, RunStart

start = RunStart(
    uid='abc123',
    time=1640000000.0,
    plan_name='scan',
    scan_id=42
)
event = Event(
    uid='def456',
    time=1640000001.0,
    descriptor_uid='ghi789',
    seq_num=1,
    data={'det': 3.14159},
    timestamps={'det': 1640000001.0},
    filled={}
)
print(start, event)