Save your readings

Right now your data disappears when the program ends. Let’s keep it.

Goal for this lesson: save the readings to a spreadsheet-style file.

CSV: the friendliest file format

A CSV file is plain text with values separated by commas. Spreadsheet programs open it directly, and Python can write it with a built-in tool, so there’s nothing new to install.

Step 1: Add a save function

Add import csv at the top of weather.py, then add save_readings and update the main block. The whole file now looks like this:

import csv

import requests

URL = (
    "https://api.open-meteo.com/v1/forecast"
    "?latitude=29.42&longitude=-98.49"
    "&hourly=temperature_2m&temperature_unit=fahrenheit&forecast_days=2&timezone=auto"
)


def get_forecast():
    response = requests.get(URL, timeout=10)
    response.raise_for_status()
    return response.json()


def hourly_readings(data, count=12):
    hourly = data["hourly"]
    return list(zip(hourly["time"], hourly["temperature_2m"]))[:count]


def save_readings(readings, path="readings.csv"):
    with open(path, "w", newline="") as f:
        writer = csv.writer(f)
        writer.writerow(["time", "temperature_f"])
        writer.writerows(readings)


if __name__ == "__main__":
    readings = hourly_readings(get_forecast())
    save_readings(readings)
    print(f"Saved {len(readings)} readings to readings.csv")

Step 2: Run it and look

python3 weather.py

You should see Saved 12 readings to readings.csv. Open readings.csv in any spreadsheet program or text editor. Your forecast is now a file you own.

Check yourself

The first row of the file should say time,temperature_f, followed by 12 rows of data. If the file is empty, make sure you saved weather.py before running it.