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Day 11: Working with APIs

In **Day 11**, you will learn how to interact with APIs (Application Programming Interfaces) using Python. APIs allow different software applications to communicate with each other.

1. Introduction to APIs

An **API** is a set of rules that allows different software programs to communicate. In simple terms, APIs define the methods and data formats that applications use to talk to each other.

RESTful APIs are commonly used, and they work over HTTP (or HTTPS).
JSON (JavaScript Object Notation) is the most common data format returned by APIs.
APIs can fetch weather data, retrieve stock prices, and much more.

2. Using `requests` Library in Python

Python provides a simple way to make HTTP requests with the `requests` library. You can easily fetch data from an API endpoint using GET requests.

Installation:

pip install requests

Basic API Request (GET method):

import requests

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

if response.status_code == 200:
    print("Request was successful.")
else:
    print(f"Failed to fetch data. Status code: {response.status_code}")

3. Handling JSON Responses

Most APIs return data in **JSON format**. To work with this data in Python, you need to parse it into Python dictionaries or lists.

import requests

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

data = response.json()
print(data[:3])  # Print the first 3 posts

4. Practical API Example: Fetching Data from OpenWeatherMap

Now let's use a real API. We'll fetch data from a public API called **OpenWeatherMap** to get weather information for a given city.

Step 1: Get an API Key

1. Visit OpenWeatherMap and create an account to generate an API key.

Step 2: Use the 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}'

response = requests.get(url)

if response.status_code == 200:
    data = response.json()
    weather = data['weather'][0]['description']
    temperature = data['main']['temp'] - 273.15  # Convert Kelvin to Celsius
    print(f"Weather in {city}: {weather}")
    print(f"Temperature: {temperature:.2f}°C")
else:
    print(f"Failed to get weather data. Status code: {response.status_code}")

Exercises:

Fetch and display data from a public API: Choose any free API and fetch data using the `requests` library.
API Error Handling: Update the weather API script to handle error codes (e.g., city not found, invalid API key).
Write a function to call the OpenWeather API: Create a function `get_weather(city)` that fetches weather data and returns the weather description and temperature.

By the end of **Day 11**, you should be comfortable with:

Understanding and working with APIs.
Fetching and processing data from APIs.
Error handling in API requests.

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