Introduction to Connexion

Connexion is a powerful Python framework that simplifies the process of building RESTful APIs. It uses OpenAPI specifications to define the API endpoints, parameters, and responses, ensuring a structured and standardized approach to API development. By leveraging Connexion, developers can focus on implementing business logic while leaving the tedious parts of API handling to the framework. Let’s dive into exploring Connexion starting with its features, API examples, and a practical app implementation.

Key Features of Connexion

• OpenAPI-based endpoint definitions for a standardized structure.
• Automatic validation of input parameters and payloads.
• Built-in support for Swagger UI for testing and documentation.
• Seamless integration with popular Python web frameworks.

Getting Started with Connexion

To start working with Connexion, you need to install it. Run the following command to install the package:

  pip install connexion

Example 1: A Basic API

Let’s define a simple API endpoint that returns a message:

OpenAPI Specification (openapi.yaml):

  openapi: "3.0.0"
  info:
    title: Simple API
    version: "1.0.0"
  paths:
    /hello:
      get:
        summary: Returns a welcome message.
        responses:
          200:
            description: A greeting message.
            content:
              application/json:
                schema:
                  type: object
                  properties:
                    message:
                      type: string

Python Code to Implement the API:

  from flask import jsonify

  def hello_world():
      return jsonify({"message": "Hello, World!"})
  
  import connexion

  app = connexion.App(__name__, specification_dir="./")
  app.add_api("openapi.yaml")

  if __name__ == "__main__":
      app.run(port=5000)

Example 2: Parameterized API

Create an API to greet users by their name:

OpenAPI Specification:

  paths:
    /greet/{name}:
      get:
        summary: Returns a personalized greeting.
        parameters:
          - in: path
            name: name
            required: true
            schema:
              type: string
        responses:
          200:
            description: A personalized message.
            content:
              application/json:
                schema:
                  type: object
                  properties:
                    message:
                      type: string

Python Implementation:

  def greet_user(name):
      return jsonify({"message": f"Hello, {name}!"})

Example 3: POST Method Handling

Let’s create an API to calculate the sum of two numbers sent via a POST request.

OpenAPI Specification:

  paths:
    /add:
      post:
        summary: Adds two numbers.
        requestBody:
          content:
            application/json:
              schema:
                type: object
                properties:
                  num1:
                    type: integer
                  num2:
                    type: integer
                required:
                  - num1
                  - num2
        responses:
          200:
            description: Sum of the numbers.
            content:
              application/json:
                schema:
                  type: object
                  properties:
                    sum:
                      type: integer

Python Implementation:

  def add_numbers(body):
      num1 = body.get("num1")
      num2 = body.get("num2")
      return jsonify({"sum": num1 + num2})

Building a Practical Application

Now, let’s combine these examples to build a complete API application:

  import connexion

  def hello_world():
      return {"message": "Hello, World!"}

  def greet_user(name):
      return {"message": f"Hello, {name}!"}

  def add_numbers(body):
      num1 = body.get("num1")
      num2 = body.get("num2")
      return {"sum": num1 + num2}

  app = connexion.App(__name__, specification_dir="./")
  app.add_api("openapi.yaml")

  if __name__ == "__main__":
      app.run(port=5000)

Create an openapi.yaml file with specifications for all the above endpoints. Run the application and access the APIs via http://127.0.0.1:5000.

Conclusion

Connexion is an excellent choice for Python developers looking to build standardized and well-documented APIs quickly. With its OpenAPI-centered approach, developers can focus on writing robust application logic while the framework handles API structure and validation. Try it out and experience the ease of API development!