Simple Weather Forecast App

Abstract

Consuming a real web API is a rite of passage, and weather is the perfect first API: free, well-documented, and instantly gratifying. In this tutorial you build a Tkinter app that queries the OpenWeatherMap API for a city’s current conditions and displays temperature, “feels like”, humidity, and a description. Then you grow it into something polished — a 5-day forecast, weather icons, °C/°F toggle, geolocation, response caching, and the kind of error handling that separates a demo from a tool.

You will leave understanding:

How to register for and use an API key safely.
The request → JSON → parse → display pipeline behind every API client.
How to read nested JSON (data["weather"][0]["description"]data["weather"][0]["description"]) without crashing.
Why you check status_codestatus_code and handle the unhappy paths first.

Prerequisites

Python 3.6 or above.
A text editor or IDE.
The requestsrequests library: pip install requestspip install requests.
A free OpenWeatherMap API key from openweathermap.org/api.
Tkinter (bundled with Python).

Getting Started

Get an API key

Sign up at openweathermap.org (free tier is plenty).
Copy your API key from the dashboard.
New keys can take a few minutes to activate — don’t panic if the first call 401s.

Create the project

Create a folder named weather-appweather-app.
Inside it, create simple_weather_forecast_app.pysimple_weather_forecast_app.py.
Install the dependency: pip install requestspip install requests.

Write the code

simple_weather_forecast_app.py

Source

simple_weather_forecast_app.py

"""
Simple Weather Forecast App
 
A Python application that fetches and displays weather forecast data. Features include:
- Fetching weather data from an API.
- Displaying the forecast in a user-friendly format.
"""
 
import requests
from tkinter import Tk, Label, Entry, Button, messagebox
 
API_KEY = "your_openweathermap_api_key"
BASE_URL = "http://api.openweathermap.org/data/2.5/weather"
 
 
class WeatherForecastApp:
    def __init__(self, root):
        self.root = root
        self.root.title("Simple Weather Forecast App")
 
        Label(root, text="Enter City Name:").grid(row=0, column=0, padx=10, pady=10)
        self.city_entry = Entry(root, width=30)
        self.city_entry.grid(row=0, column=1, padx=10, pady=10)
 
        Button(root, text="Get Weather", command=self.get_weather).grid(row=1, column=0, columnspan=2, pady=10)
 
        self.result_label = Label(root, text="", wraplength=400, justify="left")
        self.result_label.grid(row=2, column=0, columnspan=2, padx=10, pady=10)
 
    def get_weather(self):
        """Fetch weather data for the entered city."""
        city = self.city_entry.get()
        if not city:
            messagebox.showerror("Error", "Please enter a city name.")
            return
 
        params = {"q": city, "appid": API_KEY, "units": "metric"}
        try:
            response = requests.get(BASE_URL, params=params)
            data = response.json()
 
            if response.status_code == 200:
                weather = data["weather"][0]["description"].capitalize()
                temp = data["main"]["temp"]
                feels_like = data["main"]["feels_like"]
                humidity = data["main"]["humidity"]
 
                result = (
                    f"Weather in {city}:\n"
                    f"Condition: {weather}\n"
                    f"Temperature: {temp}°C\n"
                    f"Feels Like: {feels_like}°C\n"
                    f"Humidity: {humidity}%"
                )
                self.result_label.config(text=result)
            else:
                messagebox.showerror("Error", data.get("message", "Failed to fetch weather data."))
        except Exception as e:
            messagebox.showerror("Error", f"An error occurred: {e}")
 
 
def main():
    root = Tk()
    app = WeatherForecastApp(root)
    root.mainloop()
 
 
if __name__ == "__main__":
    main()

simple_weather_forecast_app.py

"""
Simple Weather Forecast App
 
A Python application that fetches and displays weather forecast data. Features include:
- Fetching weather data from an API.
- Displaying the forecast in a user-friendly format.
"""
 
import requests
from tkinter import Tk, Label, Entry, Button, messagebox
 
API_KEY = "your_openweathermap_api_key"
BASE_URL = "http://api.openweathermap.org/data/2.5/weather"
 
 
class WeatherForecastApp:
    def __init__(self, root):
        self.root = root
        self.root.title("Simple Weather Forecast App")
 
        Label(root, text="Enter City Name:").grid(row=0, column=0, padx=10, pady=10)
        self.city_entry = Entry(root, width=30)
        self.city_entry.grid(row=0, column=1, padx=10, pady=10)
 
        Button(root, text="Get Weather", command=self.get_weather).grid(row=1, column=0, columnspan=2, pady=10)
 
        self.result_label = Label(root, text="", wraplength=400, justify="left")
        self.result_label.grid(row=2, column=0, columnspan=2, padx=10, pady=10)
 
    def get_weather(self):
        """Fetch weather data for the entered city."""
        city = self.city_entry.get()
        if not city:
            messagebox.showerror("Error", "Please enter a city name.")
            return
 
        params = {"q": city, "appid": API_KEY, "units": "metric"}
        try:
            response = requests.get(BASE_URL, params=params)
            data = response.json()
 
            if response.status_code == 200:
                weather = data["weather"][0]["description"].capitalize()
                temp = data["main"]["temp"]
                feels_like = data["main"]["feels_like"]
                humidity = data["main"]["humidity"]
 
                result = (
                    f"Weather in {city}:\n"
                    f"Condition: {weather}\n"
                    f"Temperature: {temp}°C\n"
                    f"Feels Like: {feels_like}°C\n"
                    f"Humidity: {humidity}%"
                )
                self.result_label.config(text=result)
            else:
                messagebox.showerror("Error", data.get("message", "Failed to fetch weather data."))
        except Exception as e:
            messagebox.showerror("Error", f"An error occurred: {e}")
 
 
def main():
    root = Tk()
    app = WeatherForecastApp(root)
    root.mainloop()
 
 
if __name__ == "__main__":
    main()

Run it

command

C:\Users\Your Name\weather-app> python simple_weather_forecast_app.py
# Enter a city name, click "Get Weather".
# Make sure you replaced API_KEY with your real key first.

command

C:\Users\Your Name\weather-app> python simple_weather_forecast_app.py
# Enter a city name, click "Get Weather".
# Make sure you replaced API_KEY with your real key first.

Step-by-Step Explanation

1. The endpoint and key

simple_weather_forecast_app.py

API_KEY = "your_openweathermap_api_key"
BASE_URL = "http://api.openweathermap.org/data/2.5/weather"

simple_weather_forecast_app.py

API_KEY = "your_openweathermap_api_key"
BASE_URL = "http://api.openweathermap.org/data/2.5/weather"

BASE_URLBASE_URL is the “current weather” endpoint. The key authenticates you and counts against your rate limit.

2. Building the request

simple_weather_forecast_app.py

params = {"q": city, "appid": API_KEY, "units": "metric"}
response = requests.get(BASE_URL, params=params)
data = response.json()

simple_weather_forecast_app.py

params = {"q": city, "appid": API_KEY, "units": "metric"}
response = requests.get(BASE_URL, params=params)
data = response.json()

Passing a paramsparams dict lets requestsrequests build the query string for you (?q=London&appid=...&units=metric?q=London&appid=...&units=metric) and handles URL-encoding spaces and special characters. units="metric"units="metric" gives Celsius; "imperial""imperial" gives Fahrenheit.

3. Check status before parsing

simple_weather_forecast_app.py

if response.status_code == 200:
    weather = data["weather"][0]["description"].capitalize()
    temp = data["main"]["temp"]
    ...
else:
    messagebox.showerror("Error", data.get("message", "Failed to fetch weather data."))

simple_weather_forecast_app.py

if response.status_code == 200:
    weather = data["weather"][0]["description"].capitalize()
    temp = data["main"]["temp"]
    ...
else:
    messagebox.showerror("Error", data.get("message", "Failed to fetch weather data."))

This is the most important habit in API work: handle the failure path first. A typo’d city returns 404404 with a helpful messagemessage field — surface it instead of crashing on a missing key.

4. Reading nested JSON

simple_weather_forecast_app.py

data["weather"][0]["description"]   # list → first item → field
data["main"]["temp"]                # nested dict

simple_weather_forecast_app.py

data["weather"][0]["description"]   # list → first item → field
data["main"]["temp"]                # nested dict

OpenWeatherMap nests weatherweather inside a list (a place can have several conditions) and groups numbers under mainmain. Knowing the shape of the JSON is half the battle — print datadata once and study it.

Protect Your API Key

Never hard-code secrets. Use an environment variable:

config.py

import os
API_KEY = os.environ["OWM_API_KEY"]   # set OWM_API_KEY in your shell, not in code

config.py

import os
API_KEY = os.environ["OWM_API_KEY"]   # set OWM_API_KEY in your shell, not in code

command

# PowerShell
$env:OWM_API_KEY = "your_key_here"

command

# PowerShell
$env:OWM_API_KEY = "your_key_here"

This keeps the key out of screenshots, git history, and shared code.

Add a 5-Day Forecast

The forecast endpoint returns data in 3-hour steps:

forecast.py

FORECAST_URL = "http://api.openweathermap.org/data/2.5/forecast"
 
def five_day(city):
    r = requests.get(FORECAST_URL,
                     params={"q": city, "appid": API_KEY, "units": "metric"},
                     timeout=10)
    r.raise_for_status()
    # Pick the midday (12:00) reading for each day
    return [item for item in r.json()["list"] if "12:00:00" in item["dt_txt"]]

forecast.py

FORECAST_URL = "http://api.openweathermap.org/data/2.5/forecast"
 
def five_day(city):
    r = requests.get(FORECAST_URL,
                     params={"q": city, "appid": API_KEY, "units": "metric"},
                     timeout=10)
    r.raise_for_status()
    # Pick the midday (12:00) reading for each day
    return [item for item in r.json()["list"] if "12:00:00" in item["dt_txt"]]

Loop the result into five labels or a small table.

Show Weather Icons

Each condition carries an icon code:

icons.py

from tkinter import PhotoImage
import requests, io
 
icon_code = data["weather"][0]["icon"]                       # e.g. "10d"
url = f"http://openweathermap.org/img/wn/{icon_code}@2x.png"
img_bytes = requests.get(url, timeout=10).content
# Save then load, or use Pillow's ImageTk for in-memory display

icons.py

from tkinter import PhotoImage
import requests, io
 
icon_code = data["weather"][0]["icon"]                       # e.g. "10d"
url = f"http://openweathermap.org/img/wn/{icon_code}@2x.png"
img_bytes = requests.get(url, timeout=10).content
# Save then load, or use Pillow's ImageTk for in-memory display

Add a °C / °F Toggle

Store the raw value once, convert for display:

units.py

def to_fahrenheit(celsius):
    return celsius * 9 / 5 + 32
 
label.config(text=f"{temp}°C" if self.metric else f"{to_fahrenheit(temp):.1f}°F")

units.py

def to_fahrenheit(celsius):
    return celsius * 9 / 5 + 32
 
label.config(text=f"{temp}°C" if self.metric else f"{to_fahrenheit(temp):.1f}°F")

Common Mistakes

Problem	Cause	Fix
`401 Unauthorized401 Unauthorized`	Key missing, wrong, or not yet active	Check the key; wait a few minutes after signup
`KeyError: 'main'KeyError: 'main'`	Parsed JSON before checking status	Guard with `if status_code == 200if status_code == 200` first
App freezes on slow network	No `timeouttimeout`	Add `timeout=10timeout=10`; fetch on a background thread
Spaces in city name break URL	Manual string concatenation	Use the `params=params=` dict — it encodes for you
Wrong temperature scale	Forgot `unitsunits`	Set `units="metric"units="metric"` or `"imperial""imperial"`
Rate-limit errors	Polling too often	Cache responses for a few minutes

Variations to Try

Geolocation — detect the user’s city via their IP and load it on launch.
Hourly chart — plot the next 24 hours with matplotlibmatplotlib.
Favorites — save a list of cities and refresh them all at once.
Severe-weather alerts — use the One Call API’s alertsalerts field.
Background by condition — change the window color for sunny/rainy/snow.
Caching layer — store responses with a timestamp; skip the API within 10 minutes.
Voice output — read the forecast aloud (see Weather App with Voice Commands).

Real-World Applications

Travel apps — destination weather at a glance.
Agriculture & logistics — planning around conditions.
Dashboards — a weather widget on a home-automation panel.
Event planning — outdoor-event go/no-go decisions.

Educational Value

REST APIs — keys, query parameters, JSON responses.
Defensive parsing — status checks and .get().get() with defaults.
Secret management — environment variables over hard-coding.
Caching & rate limits — being a good API citizen.

Next Steps

Move the key into an environment variable.
Add a 5-day forecast and weather icons.
Implement a °C/°F toggle and response caching.
Detect the user’s city with geolocation.

Conclusion

You built a weather app that turns a city name into live conditions, then layered on a forecast, icons, unit toggles, and caching — all on top of the same request → parse → display loop you’ll reuse for every API you ever touch. The skill transfers directly: swap the endpoint and you have a stock ticker, a currency converter, or a news reader. Full source on GitHub. Explore more API projects on Python Central Hub.

If this helped you, consider buying me a coffee ☕

Buy me a coffee

Simple Weather Forecast App

Abstract

Prerequisites

Getting Started

Get an API key

Create the project

Write the code

Run it

Step-by-Step Explanation

1. The endpoint and key

2. Building the request

3. Check status before parsing

4. Reading nested JSON

Protect Your API Key

Add a 5-Day Forecast

Show Weather Icons

Add a °C / °F Toggle

Common Mistakes

Variations to Try

Real-World Applications

Educational Value

Next Steps

Conclusion

Was this page helpful?