Weather App in Python using API

What we are building

A weather app asks the user for a city, calls a weather API over the internet, and shows the current temperature and conditions. It is a great project to learn how programs fetch live data from the web using the requests library and read JSON.

The requests library

requests is the standard Python library for talking to web APIs. Install it once:

pip install requests

Then import it in your program. It lets you fetch data from a URL with a single line, requests.get(url).

Calling the API

import requests

city = "Delhi"
key = "YOUR_API_KEY"
url = f"https://api.openweathermap.org/data/2.5/weather?q={city}&appid={key}&units=metric"

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

We build the URL with the city, our API key, and units=metric for Celsius. requests.get fetches it, and .json() turns the reply into a Python dictionary.

Reading the JSON

temp = data["main"]["temp"]
weather = data["weather"][0]["description"]

print(f"Temperature in {city}: {temp} C")
print(f"Condition: {weather}")

The JSON is a nested dictionary. We reach into it by keys — data["main"]["temp"] for temperature and data["weather"][0]["description"] for the condition.

Handling errors

response = requests.get(url)
if response.status_code == 200:
    data = response.json()
    print(data["main"]["temp"], "C")
elif response.status_code == 404:
    print("City not found")
else:
    print("Error:", response.status_code)

Always check the status code. 200 means success; 404 means the city was not found; other codes mean another problem. This keeps the app from crashing on bad input.

Common mistakes

• Missing or wrong API key. The service refuses the request — sign up and use a valid key.
• Not checking the status code. A 404 or error then crashes when you read the JSON.
• Wrong JSON keys. Print the whole data first to see the exact structure.
• Forgetting units=metric. Without it, temperature comes in Kelvin, not Celsius.

Summary

• A weather app fetches live data from a weather API.
• Use the requests library and a free API key.
• requests.get(url) fetches; .json() gives a dictionary.
• Read nested keys like data["main"]["temp"].
• Check the status code (200, 404) to handle errors gracefully.

Next, understand the data format in JSON in Python, or organise it with dictionaries.