Building Mock APIs with Swagger in Python

Using Swagger, we will build a “basic Todo API“, produce a Python server stub, implement mock server logic, and execute the application. To replicate API answers, mock data for todos will be utilized. Below is the step-by-step procedure to build mock APIs with Swagger:

Step 1: Installation

In this step, we will install all the dependencies that we will require to build Mock APIs with Swagger. These are:

Install the below dependencies using pip and the following command:

pip install flask-restful
pip install flasgger

Step 2: Project Structure

Folder Structure
  |--->app.py
  |--->swagger.yml

Step 3: Create Swagger Specification

The provided Swagger YAML file (swagger.yml) defines the API structure and is used by the Swagger instance to generate Swagger UI documentation for the API. In this code, a Swagger 2.0 specification defines a Todo API with CRUD operations. It includes endpoints for retrieving all todos, creating a new todo, and managing individual todos by ID through GET, PUT, and DELETE operations.

Python3

swagger: '2.0'
info:
  title: Todo API
  description: Simple Todo API with CRUD operations
  version: '1.0'
 
paths:
  /todos:
    get:
      summary: Get all todos
      responses:
        '200':
          description: A list of todos
    post:
      summary: Create a new todo
      parameters:
        - name: todo
          in: body
          required: true
          schema:
            type: object
            properties:
              task:
                type: string
                description: The task for the new todo
              completed:
                type: boolean
                description: Whether the task is completed
      responses:
        '201':
          description: Todo created successfully
 
  /todos/{todo_id}:
    parameters:
      - name: todo_id
        in: path
        required: true
        type: integer
    get:
      summary: Get a specific todo by ID
      responses:
        '200':
          description: Todo details
        '404':
          description: Todo not found
    put:
      summary: Update a specific todo by ID
      parameters:
        - name: todo
          in: body
          required: true
          schema:
            type: object
            properties:
              task:
                type: string
                description: The updated task
              completed:
                type: boolean
                description: Whether the task is completed
      responses:
        '200':
          description: Todo updated successfully
        '404':
          description: Todo not found
    delete:
      summary: Delete a specific todo by ID
      responses:
        '200':
          description: Todo deleted successfully
        '404':
          description: Todo not found

Step 4: Implement Mock API Server Logic

In this Python code, a Flask application is created to implement a Todo API using Flask-Restful. The endpoints for managing todos are defined with GET, PUT, DELETE, POST methods, and Swagger is integrated for API documentation using the provided Swagger YAML template.

app.py

Python3

from flask import Flask, request
from flask_restful import Api, Resource
from flasgger import Swagger
 
app = Flask(__name__)
api = Api(app)
swagger = Swagger(app, template_file='swagger.yml')
 
todos = []
 
class TodoResource(Resource):
    def get(self, todo_id):
        todo = next((t for t in todos if t['id'] == todo_id), None)
        if todo:
            return todo
        else:
            return {'message': 'Todo not found'}, 404
 
    def put(self, todo_id):
        todo = next((t for t in todos if t['id'] == todo_id), None)
        if todo:
            todo['task'] = request.json.get('task', todo['task'])
            todo['completed'] = request.json.get(
                'completed', todo['completed'])
            return {'message': 'Todo updated successfully'}
        else:
            return {'message': 'Todo not found'}, 404
 
    def delete(self, todo_id):
        global todos
        todos = [t for t in todos if t['id'] != todo_id]
        return {'message': 'Todo deleted successfully'}
 
 
class TodoListResource(Resource):
    def get(self):
        return {'todos': todos}
 
    def post(self):
        new_todo = {
            'id': len(todos) + 1,
            'task': request.json['task'],
            'completed': request.json.get('completed', False)
        }
        todos.append(new_todo)
        return {'message': 'Todo created successfully'}, 201
 
api.add_resource(TodoListResource, '/todos')
api.add_resource(TodoResource, '/todos/<int:todo_id>')
 
if __name__ == '__main__':
    app.run(debug=True)

Step By Step Explanation of this Code

Import Necessary Modules

Import necessary modules and libraries, including Flask for the web framework, request for handling HTTP requests, Api and Resource from Flask-RESTful for building REST APIs, and Swagger from flasgger for integrating Swagger UI. Initialize the Flask app, API, and Swagger.

Python3

from flask import Flask, request
from flask_restful import Api, Resource
from flasgger import Swagger
 
app = Flask(__name__)
api = Api(app)
swagger = Swagger(app, template_file='swagger.yml')
todos = []

TodoResource Class

Define a class for handling individual todos (TodoResource). Implement methods for handling GET (retrieve todo by ID), PUT (update todo by ID), and DELETE (delete todo by ID) operations. The methods use the global todos list to store todo items.

Python3

class TodoResource(Resource):
    def get(self, todo_id):
        todo = next((t for t in todos if t['id'] == todo_id), None)
        if todo:
            return todo
        else:
            return {'message': 'Todo not found'}, 404
 
    def put(self, todo_id):
        todo = next((t for t in todos if t['id'] == todo_id), None)
        if todo:
            todo['task'] = request.json.get('task', todo['task'])
            todo['completed'] = request.json.get(
                'completed', todo['completed'])
            return {'message': 'Todo updated successfully'}
        else:
            return {'message': 'Todo not found'}, 404
 
    def delete(self, todo_id):
        global todos
        todos = [t for t in todos if t['id'] != todo_id]
        return {'message': 'Todo deleted successfully'}

TodoListResource Class

Define a class for handling the list of todos (TodoListResource). Implement methods for handling GET (retrieve all todos) and POST (create a new todo) operations. The POST method adds a new todo to the todos list.

Python3

class TodoListResource(Resource):
    def get(self):
        return {'todos': todos}
 
    def post(self):
        new_todo = {
            'id': len(todos) + 1,
            'task': request.json['task'],
            'completed': request.json.get('completed', False)
        }
        todos.append(new_todo)
        return {'message': 'Todo created successfully'}, 201

Resource Registration

Register the TodoListResource class to handle routes for listing and creating todos (‘/todos’) and the TodoResource class to handle routes for individual todos (‘/todos/<int:todo_id>’). Start the Flask application if the script is run directly.

Python3

api.add_resource(TodoListResource, '/todos')
api.add_resource(TodoResource, '/todos/<int:todo_id>')
 
if __name__ == '__main__':
    app.run(debug=True)

Step 5: Run the Mock Server:

Execute the Python script (python app.py). To execute the script, open a terminal and navigate to the project directory then run the command:

python app.py

Now, access Swagger UI at http://127.0.0.1:5000/apidocs/ to interact with the mock API.

http://127.0.0.1:5000/apidocs/

Output

Video Demonstration