Chapter 17: Working with APIs

APIs (Application Programming Interfaces) enable applications to communicate with each other. Python provides excellent libraries for consuming and building APIs, making it a go-to language for integrating and creating web services.

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Consuming APIs with Python

Using the requests Library

The requests library simplifies HTTP requests and is widely used for interacting with REST APIs.

Installing requests:

pip install requests

Making GET and POST Requests:

import requests

# GET request
response = requests.get("https://jsonplaceholder.typicode.com/posts/1")
print(response.json())

# POST request
payload = {"title": "foo", "body": "bar", "userId": 1}
response = requests.post("https://jsonplaceholder.typicode.com/posts", json=payload)
print(response.json())

Handling Response Codes:

if response.status_code == 200:
    print("Success:", response.json())
elif response.status_code == 404:
    print("Not Found")

Working with Authentication

Many APIs require authentication using API keys or tokens.

Example:

headers = {"Authorization": "Bearer YOUR_API_TOKEN"}
response = requests.get("https://api.example.com/data", headers=headers)
print(response.json())

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Building APIs with Python

Using Flask for API Development

Flask is a lightweight framework suitable for creating APIs.

Example:

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route("/api/data", methods=["GET"])
def get_data():
    return jsonify({"message": "Hello, World!"})

@app.route("/api/data", methods=["POST"])
def post_data():
    data = request.json
    return jsonify({"received": data})

if __name__ == "__main__":
    app.run(debug=True)

Using Django for API Development

Django REST Framework (DRF) extends Django for building APIs.

Installing DRF:

pip install djangorestframework

Creating an API with DRF:

1. Add 'rest_framework' to INSTALLED_APPS in settings.py.

2. Define a serializer in serializers.py:

   from rest_framework import serializers
   
   class ItemSerializer(serializers.Serializer):
       id = serializers.IntegerField()
       name = serializers.CharField(max_length=100)

3. Create a view in views.py:

   from rest_framework.views import APIView
   from rest_framework.response import Response
   
   class ItemView(APIView):
       def get(self, request):
           data = [
               {"id": 1, "name": "Item 1"},
               {"id": 2, "name": "Item 2"}
           ]
           return Response(data)

4. Map the view to a URL in urls.py:

   from django.urls import path
   from .views import ItemView
   
   urlpatterns = [
       path('api/items/', ItemView.as_view(), name='item-list'),
   ]

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Advanced API Techniques

Pagination

Paginate API results to handle large datasets.

@app.route("/api/items", methods=["GET"])
def get_items():
    page = int(request.args.get("page", 1))
    per_page = int(request.args.get("per_page", 10))
    items = [f"Item {i}" for i in range(1, 101)]  # Sample data
    start = (page - 1) * per_page
    end = start + per_page
    return jsonify(items[start:end])

Rate Limiting

Use tools like Flask-Limiter to restrict API usage.

pip install flask-limiter

from flask import Flask
from flask_limiter import Limiter

app = Flask(__name__)
limiter = Limiter(app, key_func=lambda: "user_key")

@app.route("/api/data")
@limiter.limit("5 per minute")
def limited_data():
    return {"message": "Limited access"}

Error Handling

Provide meaningful error messages for invalid requests.

@app.errorhandler(404)
def not_found(error):
    return jsonify({"error": "Not Found"}), 404

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Exercises

Exercise 1: Consume a Public API

Fetch and display weather data using a public API like OpenWeatherMap.

Solution:

import requests

API_KEY = "your_api_key"
url = f"http://api.openweathermap.org/data/2.5/weather?q=London&appid={API_KEY}"
response = requests.get(url)
print(response.json())

Exercise 2: Build a CRUD API with Flask

Create an API to manage a list of tasks with endpoints for adding, viewing, updating, and deleting tasks.

Solution:

from flask import Flask, jsonify, request

app = Flask(__name__)
tasks = []

@app.route("/tasks", methods=["GET"])
def get_tasks():
    return jsonify(tasks)

@app.route("/tasks", methods=["POST"])
def add_task():
    task = request.json
    tasks.append(task)
    return jsonify(task), 201

if __name__ == "__main__":
    app.run(debug=True)

Exercise 3: Build an API with Django REST Framework

Build a REST API for managing products using Django REST Framework.

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Best Practices

1. Documentation: Use tools like Swagger or Postman to document APIs.

2. Authentication: Secure APIs with OAuth, API keys, or JWTs.

3. Validation: Validate request data to prevent errors and abuse.

4. Error Handling: Return descriptive error messages with appropriate HTTP status codes.

5. Testing: Write unit tests to ensure API reliability.

In the next chapter, we will explore automation with Python, including automating tasks like file handling, web scraping, and system monitoring.