# tinker_cookbook.checkpoint_utils.CheckpointRecord

## *class* [**tinker_cookbook.checkpoint_utils.CheckpointRecord**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L29)()

A single checkpoint record stored in `checkpoints.jsonl`.

Known fields are exposed as typed attributes. `batch` is optional so that checkpoint files written by older code (or external tools that use different progress counters) can still be loaded.

Any additional user-supplied metadata from `loop_state` is preserved in `extra` so that custom keys round-trip through save/load without loss.

**Fields:**

- [**name**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L41) (*str*)
- [**batch**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L42) (*int | None*, default: `None`)
- [**epoch**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L43) (*int | None*, default: `None`)
- [**final**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L44) (*bool | None*, default: `None`)
- [**state_path**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L45) (*str | None*, default: `None`)
- [**sampler_path**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L46) (*str | None*, default: `None`)
- [**extra**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L47) (*dict[str, Any]*, default: `field(default_factory=dict)`)

### [**to_dict**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L57)()

Serialize to a dict for JSON storage.

Omits `None` optional fields. Extra metadata keys are merged into the top-level dict.

**Returns:** *dict[str, Any]* – JSON-serializable dict with known fields and any extra metadata.

### [**from_dict**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L82)(*d*)

Deserialize from a JSON-parsed dict.

Unknown keys are preserved in `extra` so that downstream metadata (e.g. `step`) round-trips without loss.

**Parameters:**

- [**d**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L82) (*dict[str, Any]*) – Dict with at least a `"name"` key.

**Returns:** *[CheckpointRecord](https://tinker-docs.thinkingmachines.ai/cookbook/api-reference/checkpoint_utils/checkpointrecord/index.md)* – Reconstructed record.

### [**has**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L104)(*key*)

Check whether a field is present (not None), including extra keys.

**Parameters:**

- [**key**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L104) (*str*) – Field name to check (known attribute or extra key).

**Returns:** *bool* – True if the field exists and is not `None`.

### [**get**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L117)(*key*, *default*)

Get a field value by name, falling back to extra, then *default*.

This provides uniform access regardless of whether a key is a known attribute or user-supplied metadata stored in `extra`.

For known fields, returns the attribute value (which may be `None` if the field is optional and unset). Returns *default* only when the key is not a known field **and** is absent from `extra`.

**Parameters:**

- [**key**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L117) (*str*) – Field name to look up (known attribute or extra key).
- [**default**](https://github.com/thinking-machines-lab/tinker-cookbook/blob/main/tinker_cookbook/checkpoint_utils.py#L117) (*Any*) – Value to return if `key` is not a known field and is absent from `extra`. If omitted, returns `None` for missing extra keys.

**Returns:** *Any* – The field value, extra value, or *default*.

## Referenced by

- [tinker_cookbook.stores.TrainingRunStore.read_checkpoint_records](https://tinker-docs.thinkingmachines.ai/cookbook/api-reference/stores/trainingrunstore/#trainingrunstore-read_checkpoint_records)