prefect.serializers

Serializer implementations for converting objects to bytes and bytes to objects.

All serializers are based on the Serializer class and include a type string that allows them to be referenced without referencing the actual class. For example, you can get often specify the JSONSerializer with the string "json". Some serializers support additional settings for configuration of serialization. These are stored on the instance so the same settings can be used to load saved objects.

All serializers must implement dumps and loads which convert objects to bytes and bytes to an object respectively.

CompressedJSONSerializer

Bases: CompressedSerializer

A compressed serializer preconfigured to use the json serializer.

Source code in src/prefect/serializers.py

class CompressedJSONSerializer(CompressedSerializer):
    """
    A compressed serializer preconfigured to use the json serializer.
    """

    type: Literal["compressed/json"] = "compressed/json"

    serializer: Serializer = Field(default_factory=JSONSerializer)

CompressedPickleSerializer

Bases: CompressedSerializer

A compressed serializer preconfigured to use the pickle serializer.

Source code in src/prefect/serializers.py

class CompressedPickleSerializer(CompressedSerializer):
    """
    A compressed serializer preconfigured to use the pickle serializer.
    """

    type: Literal["compressed/pickle"] = "compressed/pickle"

    serializer: Serializer = Field(default_factory=PickleSerializer)

CompressedSerializer

Bases: Serializer

Wraps another serializer, compressing its output. Uses lzma by default. See compressionlib for using alternative libraries.

Attributes:

Name	Type	Description
serializer	Serializer	The serializer to use before compression.
compressionlib	str	The import path of a compression module to use. Must have methods compress(bytes) -> bytes and decompress(bytes) -> bytes.
level	str	If not null, the level of compression to pass to compress.

Source code in src/prefect/serializers.py

class CompressedSerializer(Serializer):
    """
    Wraps another serializer, compressing its output.
    Uses `lzma` by default. See `compressionlib` for using alternative libraries.

    Attributes:
        serializer: The serializer to use before compression.
        compressionlib: The import path of a compression module to use.
            Must have methods `compress(bytes) -> bytes` and `decompress(bytes) -> bytes`.
        level: If not null, the level of compression to pass to `compress`.
    """

    type: Literal["compressed"] = "compressed"

    serializer: Serializer
    compressionlib: str = "lzma"

    @field_validator("serializer", mode="before")
    def validate_serializer(cls, value):
        return cast_type_names_to_serializers(value)

    @field_validator("compressionlib")
    def check_compressionlib(cls, value):
        return validate_compressionlib(value)

    def dumps(self, obj: Any) -> bytes:
        blob = self.serializer.dumps(obj)
        compressor = from_qualified_name(self.compressionlib)
        return base64.encodebytes(compressor.compress(blob))

    def loads(self, blob: bytes) -> Any:
        compressor = from_qualified_name(self.compressionlib)
        uncompressed = compressor.decompress(base64.decodebytes(blob))
        return self.serializer.loads(uncompressed)

JSONSerializer

Bases: Serializer

Serializes data to JSON.

Input types must be compatible with the stdlib json library.

Wraps the json library to serialize to UTF-8 bytes instead of string types.

Source code in src/prefect/serializers.py

class JSONSerializer(Serializer):
    """
    Serializes data to JSON.

    Input types must be compatible with the stdlib json library.

    Wraps the `json` library to serialize to UTF-8 bytes instead of string types.
    """

    type: Literal["json"] = "json"

    jsonlib: str = "json"
    object_encoder: Optional[str] = Field(
        default="prefect.serializers.prefect_json_object_encoder",
        description=(
            "An optional callable to use when serializing objects that are not "
            "supported by the JSON encoder. By default, this is set to a callable that "
            "adds support for all types supported by "
        ),
    )
    object_decoder: Optional[str] = Field(
        default="prefect.serializers.prefect_json_object_decoder",
        description=(
            "An optional callable to use when deserializing objects. This callable "
            "is passed each dictionary encountered during JSON deserialization. "
            "By default, this is set to a callable that deserializes content created "
            "by our default `object_encoder`."
        ),
    )
    dumps_kwargs: Dict[str, Any] = Field(default_factory=dict)
    loads_kwargs: Dict[str, Any] = Field(default_factory=dict)

    @field_validator("dumps_kwargs")
    def dumps_kwargs_cannot_contain_default(cls, value):
        return validate_dump_kwargs(value)

    @field_validator("loads_kwargs")
    def loads_kwargs_cannot_contain_object_hook(cls, value):
        return validate_load_kwargs(value)

    def dumps(self, data: Any) -> bytes:
        json = from_qualified_name(self.jsonlib)
        kwargs = self.dumps_kwargs.copy()
        if self.object_encoder:
            kwargs["default"] = from_qualified_name(self.object_encoder)
        result = json.dumps(data, **kwargs)
        if isinstance(result, str):
            # The standard library returns str but others may return bytes directly
            result = result.encode()
        return result

    def loads(self, blob: bytes) -> Any:
        json = from_qualified_name(self.jsonlib)
        kwargs = self.loads_kwargs.copy()
        if self.object_decoder:
            kwargs["object_hook"] = from_qualified_name(self.object_decoder)
        return json.loads(blob.decode(), **kwargs)

PickleSerializer

Bases: Serializer

Serializes objects using the pickle protocol.

• Uses cloudpickle by default. See picklelib for using alternative libraries.
• Stores the version of the pickle library to check for compatibility during deserialization.
• Wraps pickles in base64 for safe transmission.

Source code in src/prefect/serializers.py

class PickleSerializer(Serializer):
    """
    Serializes objects using the pickle protocol.

    - Uses `cloudpickle` by default. See `picklelib` for using alternative libraries.
    - Stores the version of the pickle library to check for compatibility during
        deserialization.
    - Wraps pickles in base64 for safe transmission.
    """

    type: Literal["pickle"] = "pickle"

    picklelib: str = "cloudpickle"
    picklelib_version: Optional[str] = None

    @field_validator("picklelib")
    def check_picklelib(cls, value):
        return validate_picklelib(value)

    # @model_validator(mode="before")
    # def check_picklelib_version(cls, values):
    #     return validate_picklelib_version(values)

    def dumps(self, obj: Any) -> bytes:
        pickler = from_qualified_name(self.picklelib)
        blob = pickler.dumps(obj)
        return base64.encodebytes(blob)

    def loads(self, blob: bytes) -> Any:
        pickler = from_qualified_name(self.picklelib)
        return pickler.loads(base64.decodebytes(blob))

Serializer

Bases: BaseModel, Generic[D], ABC

A serializer that can encode objects of type 'D' into bytes.

Source code in src/prefect/serializers.py

@register_base_type
class Serializer(BaseModel, Generic[D], abc.ABC):
    """
    A serializer that can encode objects of type 'D' into bytes.
    """

    def __init__(self, **data: Any) -> None:
        type_string = get_dispatch_key(self) if type(self) != Serializer else "__base__"
        data.setdefault("type", type_string)
        super().__init__(**data)

    def __new__(cls: Type[Self], **kwargs) -> Self:
        if "type" in kwargs:
            try:
                subcls = lookup_type(cls, dispatch_key=kwargs["type"])
            except KeyError as exc:
                raise ValidationError(errors=[exc], model=cls)

            return super().__new__(subcls)
        else:
            return super().__new__(cls)

    type: str

    @abc.abstractmethod
    def dumps(self, obj: D) -> bytes:
        """Encode the object into a blob of bytes."""

    @abc.abstractmethod
    def loads(self, blob: bytes) -> D:
        """Decode the blob of bytes into an object."""

    model_config = ConfigDict(extra="forbid")

    @classmethod
    def __dispatch_key__(cls) -> str:
        type_str = cls.model_fields["type"].default
        return type_str if isinstance(type_str, str) else None

dumps(obj) abstractmethod

Encode the object into a blob of bytes.

Source code in src/prefect/serializers.py

@abc.abstractmethod
def dumps(self, obj: D) -> bytes:
    """Encode the object into a blob of bytes."""

loads(blob) abstractmethod

Decode the blob of bytes into an object.

Source code in src/prefect/serializers.py

@abc.abstractmethod
def loads(self, blob: bytes) -> D:
    """Decode the blob of bytes into an object."""

prefect_json_object_decoder(result)

JSONDecoder.object_hook for decoding objects from JSON when previously encoded with prefect_json_object_encoder

Source code in src/prefect/serializers.py

def prefect_json_object_decoder(result: dict):
    """
    `JSONDecoder.object_hook` for decoding objects from JSON when previously encoded
    with `prefect_json_object_encoder`
    """
    if "__class__" in result:
        return TypeAdapter(from_qualified_name(result["__class__"])).validate_python(
            result["data"]
        )
    elif "__exc_type__" in result:
        return from_qualified_name(result["__exc_type__"])(result["message"])
    else:
        return result

prefect_json_object_encoder(obj)

JSONEncoder.default for encoding objects into JSON with extended type support.

Raises a TypeError to fallback on other encoders on failure.

Source code in src/prefect/serializers.py

def prefect_json_object_encoder(obj: Any) -> Any:
    """
    `JSONEncoder.default` for encoding objects into JSON with extended type support.

    Raises a `TypeError` to fallback on other encoders on failure.
    """
    if isinstance(obj, BaseException):
        return {"__exc_type__": to_qualified_name(obj.__class__), "message": str(obj)}
    else:
        return {
            "__class__": to_qualified_name(obj.__class__),
            "data": custom_pydantic_encoder({}, obj),
        }