Excel file format cannot be determined, you must specify an engine manually.

When you encounter the error message “excel file format cannot be determined, you must specify an engine manually” while working with an Excel file, it means that the library or tool you are using to read or manipulate Excel files could not automatically detect the correct file format.

To resolve this issue, you need to explicitly specify the engine or library to use for parsing the Excel file. Different libraries may have different ways to specify the engine, so let’s discuss a couple of examples:

Example 1:
If you are using the Pandas library in Python, you can encounter this error while using the `read_excel` function. To specify the engine, you can pass the `engine` parameter with a valid engine name. The two commonly used engines are ‘xlrd’ and ‘openpyxl’. Here’s an example:

    import pandas as pd
    df = pd.read_excel('file.xlsx', engine='xlrd')
  

In the above example, we specified the ‘xlrd’ engine explicitly. If it doesn’t work, you can try using the ‘openpyxl’ engine instead.

Example 2:
If you are using the PHPExcel library in PHP, you might face this error while trying to load an Excel file. To specify the engine manually, you need to set the `PHPExcel_Settings::setZipClass()` method with the appropriate class name. Here’s an example:

    require_once 'PHPExcel/IOFactory.php';
    $inputFileName = 'file.xlsx';
    
    $zipClass = 'ZipArchive'; // or 'PclZip' if available
    
    PHPExcel_Settings::setZipClass($zipClass);
    $objPHPExcel = PHPExcel_IOFactory::load($inputFileName);
  

In the above example, we set the `$zipClass` variable to either ‘ZipArchive’ or ‘PclZip’ based on availability. This helps PHPExcel in determining the correct engine to use for reading the Excel file.

These are just a couple of examples showcasing how to specify the engine manually for different libraries. The specific library or tool you are using may have its own way of handling this situation. You can refer to the documentation of the library or tool to find the appropriate method or parameter to specify the engine when encountering this error.