Sales per Region

Context. A store manager has a table of orders, each tagged with a region. They want the total sales for each region.

Your task. Write sales_per_region(df) that returns a pandas Series indexed by region, where each value is the sum of the amount column for that region.

Example.

Input df:

Returns a Series:

region
North    130
South     50

Notes.

• Region order in the result doesn't matter — we only compare keys → values.
• Empty DataFrame → return an empty Series.
• A region with only one order is still a valid group (its total is just that one value).