pandas
Also written as DataFrame, Polars
The Python library for loading, cleaning and reshaping tabular data — the everyday workhorse of anyone who works with data in Python.
Think of it like
A spreadsheet you drive with code instead of a mouse, so the same clean-up runs again tomorrow without you.
Junior or senior?
Table-stakes for any data role, so its presence says little. Scale is what matters: someone who has hit the point where the data no longer fits in memory has learned something real.
Ask them
“What did you do the first time your data was too big for pandas to handle?”
Sounds like real experience
Describes hitting a memory limit and moving to a database, Spark, or chunked processing, and can say why they picked that route.
Probe further if
Has never worked with data beyond a few thousand rows, or treats pandas as interchangeable with a spreadsheet.