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Appending to CSV Files

Sometimes you want to create a brand-new CSV file, but sometimes you want to keep the existing file and append more rows to the end.

If you open a file in "a" (append) mode, Python appends new content instead of overwriting the file:

with open("posts.csv", "a", newline="") as file:
    writer = csv.DictWriter(file, fieldnames=["post_id", "likes", "published"])
    writer.writerow({"post_id": "post-12", "likes": "350", "published": "true"})

When appending, don't call writeheader() again unless you're creating a brand-new file. You could wind up with duplicate headers in the middle of your CSV:

post_id,likes,published
post-01,1200,true
post_id,likes,published
post-12,350,true

Assignment

The ops team has an existing CSV file with device data. You need to append new readings without overwriting what's already there.

Complete the append_multiple_readings function. It accepts a list of device dictionaries and appends them to an existing CSV file at the provided path.

Use with open() to open the file in append mode ("a") with newline="".
Use csv.DictWriter with fieldnames in this order: device_id, temperature, online.
Write all the device rows, not a header row.