Data Processing

Why Your Pandas groupby Aggregation Is Returning Wrong Numbers

Your groupby().sum() looks right but the numbers are off. Before you blame the data, check these common Pandas aggregation traps — duplicate rows, NaN handling, dtype coercion, and more — that silently corrupt your results.

Jun 19, 2026 9m read 👁 1

Fixing Python xlrd Errors When Opening xlsx Files After Version 2.0

Getting "Excel xlsx file; not supported" after upgrading xlrd? Since xlrd 2.0 removed support for xlsx files, many Python scripts suddenly broke. Learn why this happens, how to fix it using openpyxl, and the best approaches for reading modern Excel files in Python.

Jun 18, 2026 4m read 👁 5