Legacy .xls in Python

Old import screens, ERPs and reporting tools still require, or produce, Excel 97-2003 .xls files. Python's libraries split the format awkwardly, and many files named .xls aren't .xls at all.

1. Find out what the file really is

python scripts/sniff_spreadsheet.py export.xls other.xlsx

It reads the file's bytes, not its extension, and names a reader. It's read-only and uses only the standard library. Common findings: