Lesson 27: API Requests in Python

🎯 Lesson Objective

To learn how to interact with APIs using Python, send requests, handle responses, and work with data from external sources such as web services or third-party platforms.

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🧩 1. What Is an API?

API (Application Programming Interface) allows one program to communicate with another.

• APIs are commonly used to fetch data from web services, interact with databases, or control external applications.
• HTTP methods are mostly used:
  • GET → Retrieve data
  • POST → Send data
  • PUT → Update data
  • DELETE → Delete data

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⚙️ 2. Python Requests Module

The requests module is the most popular library for working with HTTP APIs in Python.

✅ Install if not already installed:

pip install requests

Import the module:

import requests

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🔹 3. Sending a GET Request

GET requests are used to retrieve data from a server.

import requests

url = "https://jsonplaceholder.typicode.com/posts/1"
response = requests.get(url)

# Check response status
print("Status Code:", response.status_code)

# Get JSON data
data = response.json()
print(data)

Output Example:

{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati",
  "body": "quia et suscipit..."
}

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🔹 4. Sending a POST Request

POST requests send data to the server.

url = "https://jsonplaceholder.typicode.com/posts"
payload = {
    "title": "Python API",
    "body": "This is a test post",
    "userId": 1
}

response = requests.post(url, json=payload)
print("Status Code:", response.status_code)
print(response.json())

Output Example:

{
  "title": "Python API",
  "body": "This is a test post",
  "userId": 1,
  "id": 101
}

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🔹 5. Adding Headers

Sometimes APIs require headers for authentication or content type.

url = "https://jsonplaceholder.typicode.com/posts"
headers = {"Content-Type": "application/json"}

response = requests.get(url, headers=headers)
print(response.json()[0])

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🔹 6. Handling Query Parameters

Many APIs accept query parameters to filter or sort data.

url = "https://jsonplaceholder.typicode.com/posts"
params = {"userId": 1}

response = requests.get(url, params=params)
posts = response.json()

for post in posts:
    print(f"{post['id']}: {post['title']}")

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🔹 7. Error Handling in API Requests

Always handle errors like network failures or invalid responses.

try:
    response = requests.get("https://jsonplaceholder.typicode.com/posts/1")
    response.raise_for_status()  # Raises HTTPError for bad responses
    data = response.json()
    print(data)
except requests.exceptions.HTTPError as err:
    print("HTTP error occurred:", err)
except requests.exceptions.ConnectionError as err:
    print("Connection error occurred:", err)
except requests.exceptions.Timeout as err:
    print("Request timed out:", err)
except requests.exceptions.RequestException as err:
    print("An error occurred:", err)

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🔹 8. Working with JSON Data

API responses are usually JSON, so you can manipulate them as dictionaries or lists.

import requests

url = "https://jsonplaceholder.typicode.com/users"
response = requests.get(url)
users = response.json()

for user in users:
    print(f"Name: {user['name']}, Email: {user['email']}, City: {user['address']['city']}")

Output Example:

Name: Leanne Graham, Email: Sincere@april.biz, City: Gwenborough
Name: Ervin Howell, Email: Shanna@melissa.tv, City: Wisokyburgh
...

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🔹 9. Real-Life Example – Weather API

Fetching weather data from OpenWeatherMap API.

import requests

api_key = "YOUR_API_KEY"
city = "London"
url = f"http://api.openweathermap.org/data/2.5/weather?q={city}&appid={api_key}&units=metric"

response = requests.get(url)
data = response.json()

if response.status_code == 200:
    print(f"City: {data['name']}")
    print(f"Temperature: {data['main']['temp']}°C")
    print(f"Weather: {data['weather'][0]['description']}")
else:
    print("Error:", data["message"])

Output Example:

City: London
Temperature: 18°C
Weather: light rain

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🔹 10. Authentication with APIs

Some APIs require authentication, e.g., API keys, tokens, or OAuth.

url = "https://api.example.com/data"
headers = {"Authorization": "Bearer YOUR_ACCESS_TOKEN"}

response = requests.get(url, headers=headers)
print(response.json())

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🔹 11. Advanced Techniques

• Timeouts: Avoid waiting forever for a server response.

requests.get(url, timeout=5)  # 5 seconds max

• Retrying Failed Requests: Use requests.adapters for automatic retries.
• Streaming Large Data: Use stream=True for big files to avoid memory overload.

with requests.get("https://example.com/largefile", stream=True) as r:
    with open("largefile.zip", "wb") as f:
        for chunk in r.iter_content(chunk_size=8192):
            f.write(chunk)

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