Resolving the zipfile.BadZipFile Error When Using the openpyxl Engine in Python

Learn how to resolve the `zipfile.BadZipFile: File is not a zip file` error while using the `openpyxl` engine in your Python script for reading Excel files from S3.
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Troubleshooting the zipfile.BadZipFile Error in Python

If you've been working with Excel files in Python and have encountered the error zipfile.BadZipFile: File is not a zip file, you're certainly not alone. This common issue usually arises when dealing with Excel files stored in S3 using libraries like pandas and openpyxl. In this guide, we'll explore this error in detail, examine its causes, and provide a straightforward solution to resolve it.

Understanding the Issue

In your script, you are attempting to read Excel files from an S3 bucket using pandas. The error occurs while trying to specify the openpyxl engine to read Excel files. Here’s a brief overview of the code snippet that leads to the error:

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

When this line is executed, it leads to the following error message:

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

This error typically indicates that the file being read does not have the expected zip format that Excel files should have. It’s crucial to know that openpyxl is designed to work with .xlsx files, which are essentially zipped collections of XML files.

What Causes the BadZipFile Error?

The root cause of this error is due to the handling of the obj['Body'] stream when reading it multiple times. Specifically, the issue arises from:

Multiple Reads: The code reads the content of obj['Body'] multiple times.

Empty Stream on Second Read: After the first read, the stream pointer is at the end, and subsequent reads attempt to read nothing, resulting in an empty byte string.

Solution to the Problem

To solve the zipfile.BadZipFile error, you'll want to avoid reading from the S3 stream multiple times. Instead, you should read the stream once, store it, and then manipulate it as needed. Below are the steps to correct this:

Step-by-Step Breakdown

Read the S3 Object Once:
Use BytesIO to store the contents of the S3 object after reading it the first time.

Rewind the BytesIO Stream:
After the first read, use the seek(0) method to rewind the stream back to the beginning so it can be read again.

Here’s how you can apply this solution in your code:

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

Key Points to Remember

Always ensure to read from the data stream only once unless you reset the pointer.

Use seek(0) to go back to the beginning of the BytesIO stream after reading it.

This approach not only resolves the current error but makes your code cleaner and more efficient.

Conclusion

The zipfile.BadZipFile: File is not a zip file error while using the openpyxl engine in pandas can be a hindrance, but with a few adjustments to your reading strategy, you can overcome it easily. By reading the S3 data into a BytesIO object once and rewinding the stream, you're able to use the data effectively without encountering this frustrating issue.

If you have any questions or need further clarification on handling Excel files in Python, feel free to ask!