Which of the following snippets shows filtering by location and month?

• A. for each row in data: if row.location == 'X' and row.month != 'Y': process row
• B. for each row in data: if row.location != 'X' or row.month == 'Y': process row
• C. for each row in data: if row.location == 'X' and row.month == 'Y': process row
• D. for each row in data: if row.location == 'X' or row.month == 'Y': process row

Answer: (C)

Filtering by location and month means you keep a row only if both conditions are true at the same time. The snippet that checks row.location == 'X' and row.month == 'Y' requires location to be X and month to be Y together, so only rows that match both will be processed.

Using month != 'Y' would filter differently, allowing any other month for the same location, which isn’t the exact dual condition we want. Using OR would include any row that either has a different location or has the month Y, pulling in many more rows than just the exact match for both criteria. The same idea applies to other OR combinations—they don’t enforce both requirements simultaneously.

So the correct approach is the one that combines both checks with and, ensuring both location and month match.