How to Type a Variable in FastAPI-SwaggerUI with a Hyphen in Its Name?

Discover how to easily handle variables with hyphens in FastAPI by using Pydantic’s Field alias feature for clean SwaggerUI representation.
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How to Type a Variable in FastAPI-SwaggerUI with a Hyphen in Its Name?

FastAPI is an excellent framework for building APIs quickly and efficiently, but it follows Python's variable naming rules. So, if you're looking to create an API response that includes a variable with a hyphen in its name, you might run into some challenges. Specifically, Python doesn't allow hyphens in variable names, which can limit your flexibility when designing your API's response structure. However, with Pydantic and FastAPI, there’s a way around this!

The Problem: Hyphens in Variable Names

When you send a request to your FastAPI application, you might want the response to contain fields that are easily readable and include hyphens, such as var-name1. However, if you attempt to use hyphens directly, you'll encounter a syntax error because Python treats hyphens as arithmetic subtraction operators. For example, if you want to structure your response like this:

[[See Video to Reveal this Text or Code Snippet]]

It becomes clear that we need a method to achieve this without violating Python's naming conventions.

The Solution: Using Pydantic's Field Alias

To create a Pydantic model that allows you to use a hyphen in your JSON response but still keep a valid Python variable name, you can utilize the Field class to set an alias. Here’s how to adjust your Response model:

Step-by-Step Instructions

Import the Necessary Libraries:
First, ensure you have imported Field from pydantic:

[[See Video to Reveal this Text or Code Snippet]]

Define the Response Model:
Modify your existing response model to include the alias feature of Pydantic's Field class. Here’s how your updated response model should look:

[[See Video to Reveal this Text or Code Snippet]]

Understand the Configuration:

The alias="var-name" within the Field function specifies how this variable will appear in the JSON output.

The Config subclass with allow_population_by_field_name = True allows you to instantiate your Pydantic model using either the alias or the actual variable name. This is essential because it allows you to still manipulate the model in your Python code using the valid variable name var_name while responding with the desired var-name in your API output.

Example Usage

Now, your API can return a response with a variable like this:

[[See Video to Reveal this Text or Code Snippet]]

When you call this endpoint and pass a string, the JSON response will output:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By using Pydantic's Field alias feature, you can effectively create APIs in FastAPI that respond with field names containing hyphens while adhering to Python's variable naming constraints. This method enhances the readability of your API responses and ensures that users can effortlessly interact with your API while benefiting from a clean and beautiful Swagger UI documentation.

Make sure to explore more about FastAPI and Pydantic, as they offer numerous other features to simplify API development and enhance functionality!