The `xlrd.biffh.XLRDError: Excel xlsx file; not supported` error is a common issue faced by Python developers working with spreadsheet data, particularly when using the `xlrd` library. This error indicates a mismatch between the file type being read and the support provided by the `xlrd` library. In this article, we will dive into the details of this error, explore its causes, and provide solutions.

Understanding the Error

What is `xlrd`?

`xlrd` is a Python library used for reading data and formatting information from Excel files in the `.xls` format. Historically, it supported both `.xls` and `.xlsx` formats, although its primary focus and compatibility have been with `.xls` files.

The Error Explained

The error message itself: `xlrd.biffh.XLRDError: Excel xlsx file; not supported` suggests that the `xlrd` library is attempting to open an `.xlsx` file, which it no longer supports.

Cause of the Error

The root cause of this error lies in updates made to the `xlrd` library. As of version 2.0.0, `xlrd` dropped support for `.xlsx` files for security reasons related to the Excel binary format. Consequently, attempting to open an `.xlsx` file using `xlrd` will throw this error.

Solutions to the Error

Alternative Libraries

Given that `xlrd` no longer supports `.xlsx` files, developers must turn to alternatives. Here are some popular Python libraries that support `.xlsx` files:

1. `openpyxl`: A Python library that allows you to read and write `.xlsx` files. It is widely used and actively maintained.
2. `pandas`: A powerful data manipulation library, which can read `.xlsx` files using the `pd.read_excel()` method. By default, this method relies on `openpyxl` if the file is `.xlsx`.
3. `pyxlsb`: Specifically designed for reading and writing `.xlsb` (Excel Binary) files, although not a solution for `.xlsx` files directly, it's noteworthy for different Excel formats.

Code Example: Migrating to `openpyxl`

Here’s how you can modify your code to use `openpyxl` instead of `xlrd` for `.xlsx` files: