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Learn how to append new data to an existing CSV file in Python without overwriting previous entries. This guide provides simple coding solutions for beginners.
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This video is based on the question https://stackoverflow.com/q/68322635/ asked by the user 'Equinox' ( https://stackoverflow.com/u/16072563/ ) and on the answer https://stackoverflow.com/a/68322651/ provided by the user 'Ben Y' ( https://stackoverflow.com/u/9005114/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Writing to an Existing CSV File in Python: Avoiding Overwrites

When working with files in Python, especially CSV files, one common challenge is ensuring that data is added to the file without unintentionally overwriting existing content. If you're facing this issue, where your program writes to a CSV file but overwrites previous entries, you're not alone. Let's explore why this happens and how you can easily fix it.

The Problem Explained

In your initial attempt to write to a CSV file, you used the following code snippet:

[[See Video to Reveal this Text or Code Snippet]]

This code consistently overwrites the existing file contents because of the mode 'w'. When you open a file in write mode, Python truncates the file and removes all its previous content, leading to the loss of earlier entries.

The Solution: Use Append Mode

To keep your existing data while adding new entries, you should open the file in append mode ('a'). This allows you to add new rows at the end of the file without losing what's already there. Here's how to modify your code:

Step-by-Step Guide to Append Data

Change the File Mode: Replace 'w' with 'a' when opening the file.

Avoid Adding Headers Repeatedly: If your CSV file already contains headers, make sure not to write them each time you append data.

Here’s an updated version of your function:

[[See Video to Reveal this Text or Code Snippet]]

Key Points to Remember

Use Append Mode ('a'): This ensures that each time you run your function, it adds new data to the bottom of your existing file.

Conditional Header Writing: Include logic to write headers only if the file is being created for the first time to avoid duplicating header rows.

Conclusion

By using the 'a' mode for opening your CSV file, you can easily add multiple entries without losing previously stored information. This simple adjustment makes it easy to manage growing datasets in Python, especially when utilizing the CSV file format for data storage.

Feel free to use this improved approach to ensure your CSV file continues growing as intended with each new entry. Happy coding!