Enum type

At times, you might need to limit the acceptable values for inputs or outputs to a predefined set. This common requirement is usually met by using Enum types in programming languages.

You can create a Python Enum type and utilize it as an input or output for a task. Union will automatically convert it and constrain the inputs and outputs to the predefined set of values.

Currently, only string values are supported as valid Enum values. Union.ai assumes the first value in the list as the default, and Enum types cannot be optional. Therefore, when defining Enums, it’s important to design them with the first value as a valid default.

We define an Enum and a simple coffee maker workflow that accepts an order and brews coffee ☕️ accordingly. The assumption is that the coffee maker only understands Enum inputs:

        
    
# coffee_maker.py

from enum import Enum

import union

class Coffee(Enum):
    ESPRESSO = "espresso"
    AMERICANO = "americano"
    LATTE = "latte"
    CAPPUCCINO = "cappucccino"


@union.task
def take_order(coffee: str) -> Coffee:
    return Coffee(coffee)


@union.task
def prep_order(coffee_enum: Coffee) -> str:
    return f"Preparing {coffee_enum.value} ..."


@union.workflow
def coffee_maker(coffee: str) -> str:
    coffee_enum = take_order(coffee=coffee)
    return prep_order(coffee_enum=coffee_enum)


# The workflow can also accept an enum value
@union.workflow
def coffee_maker_enum(coffee_enum: Coffee) -> str:
    return prep_order(coffee_enum=coffee_enum)

You can specify value for the parameter coffee_enum on run:

$ union run coffee_maker.py coffee_maker_enum --coffee_enum="latte"