Using Custom Python ObjectsΒΆ

Flyte supports passing JSONs between tasks. But, to simplify the usage for the users and introduce type-safety, flytekit supports passing custom data objects between tasks. Currently only dataclasses that are decorated with @dataclasses_json are supported.

This example shows how users can serialize custom JSON-compatible dataclasses between successive tasks using the excellent dataclasses_json library

import typing
from dataclasses import dataclass

from dataclasses_json import dataclass_json
from flytekit import task, workflow

This Datum is a user defined complex type, which can be used to pass complex data between tasks. Moreover, users can also pass this data between different languages and also input through the Flyteconsole as a raw JSON.


Only other supported types can be nested in this class, for example it can only contain other @dataclass_json annotated dataclasses if you want to use complex classes. Arbitrary classes will cause a failure.


All variables in DataClasses should be annotated with their type. Failure to do should will result in an error

class Datum(object):
    Example of a simple custom class that is modeled as a dataclass

    x: int
    y: str
    z: typing.Dict[int, str]

Once declared, dataclasses can be returned as outputs or accepted as inputs

def stringify(x: int) -> Datum:
    A dataclass return will be regarded as a complex single json return.
    return Datum(x=x, y=str(x), z={x: str(x)})

def add(x: Datum, y: Datum) -> Datum:
    Flytekit will automatically convert the passed in json into a DataClass. If the structures dont match, it will raise
    a runtime failure
    return Datum(x=x.x + y.x, y=x.y + y.y, z=x.z)

Workflow creation remains identical

def wf(x: int, y: int) -> Datum:
    Dataclasses (JSON) can be returned from a workflow as well.
    return add(x=stringify(x=x), y=stringify(x=y))

if __name__ == "__main__":
    This workflow can be run locally. During local execution also, the dataclasses will be marshalled to and from json.
    wf(x=10, y=20)

Total running time of the script: ( 0 minutes 0.000 seconds)

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