Marshmallow-Enum: Simplifying Enum Fields for Marshmallow

Enums are a powerful way to define a set of distinct values within a program. They provide clarity, maintainability, and robustness to our code. However, when it comes to integrating Enum fields with Marshmallow, things can get a bit tricky. That’s where Marshmallow-Enum comes to the rescue.

Marshmallow-Enum is a package that offers seamless integration of Enum fields with Marshmallow, making serialization and deserialization a breeze. In this article, we will explore the key features and functionalities of Marshmallow-Enum and discuss how it simplifies the usage of Enum fields in Marshmallow schemas.

Installation

Before diving into the specifics of Marshmallow-Enum, let’s start by installing the package. With just a single pip command, you can have Marshmallow-Enum up and running in your Python environment:

pip install --user marshmallow_enum

If you’re using a version before 3.4, make sure to also install the enum34 package.

Integrating Marshmallow-Enum

To start using Marshmallow-Enum, you need to have an existing Enum defined in your code. Let’s take an example of a StopLight Enum:

from enum import Enum

class StopLight(Enum):
green = 1
yellow = 2
red = 3

Once you have your Enum ready, you can declare it as a field in a Marshmallow schema using the EnumField provided by Marshmallow-Enum:

from marshmallow import Schema
from marshmallow_enum import EnumField

class TrafficStop(Schema):
light_color = EnumField(StopLight)

By default, the EnumField will load and dump based on the _name_ given to an enum value. For example:

schema = TrafficStop()
schema.dump({'light_color': StopLight.red}).data
# {'light_color': 'red'}

schema.load({'light_color': 'red'}).data
# {'light_color': StopLight.red}

Customizing Loading and Dumping Behavior

Marshmallow-Enum provides several options to customize the loading and dumping behavior of Enum values:

1. Setting by_value=True: This option causes both dumping and loading to use the value of the enum.
2. Setting load_by=EnumField.VALUE: This option makes loading use the value of the enum.
3. Setting dump_by=EnumField.VALUE: This option makes dumping use the value of the enum.

If load_by or dump_by are left unset, they will follow from by_value. Additionally, there is EnumField.NAME, which explicitly defines the desired load and dump behavior—equivalent to leaving both by_value and either load_by and/or dump_by unset.

Custom Error Message

Marshmallow-Enum also allows for custom error messages when handling Enum fields. You can provide a custom error message using the error keyword argument. The error message can include placeholders that will be replaced with relevant information:

• {input}: The value provided to the schema field.
• {names}: The names of the individual enum members.
• {values}: The values of the individual enum members.

Please note that certain placeholders ({name}, {value}, and {choices}) are deprecated and will be removed in the future.

Real-World Use Cases

Now that we have explored the features and customization options offered by Marshmallow-Enum, let’s delve into some real-world use cases.

• API Development: When building API endpoints, Enum fields often represent different options or states that an object can have. Marshmallow-Enum simplifies the JSON serialization and deserialization of these Enum fields, ensuring seamless communication with external systems.
• Data Validation: Enum fields can be used to enforce specific choices or constraints on the data being processed. Marshmallow-Enum provides an intuitive way to validate and transform data by mapping them to the corresponding Enum values.
• Configuration Management: In configuration management systems, Enum fields are commonly used to define settings and options. With Marshmallow-Enum, you can effortlessly handle Enum fields in your configuration schemas, improving the robustness and maintainability of your code.

Conclusion

Marshmallow-Enum simplifies the integration of Enum fields with Marshmallow, making serialization and deserialization a breeze. By providing customizable loading and dumping behaviors, Marshmallow-Enum gives you full control over how Enum values are represented in your schemas. With real-world use cases in API development, data validation, and configuration management, Marshmallow-Enum offers a versatile solution for working with Enum fields in your Python projects.

So what are you waiting for? Install Marshmallow-Enum today and unlock the full potential of Enum fields in Marshmallow!