Level 5 · Lighting in a price band

Ranges with between

“From $50 to $200” is a range. You could write two comparisons:

(products["unit_price"] >= 50) & (products["unit_price"] <= 200)

between says the same thing more clearly:

products["unit_price"].between(50, 200)

By default both ends are included, matching how people usually speak about ranges. Change it with inclusive="left", "right" or "neither" when the brief says “under $200” or “over $50”. Always check which one the brief means. The Harbor & Pine catalog has products at exactly $189 and $159, and you’ll find edge cases like a $200 product in real catalogs all the time.

between works on dates too, which you’ll use constantly:

orders[orders["order_date"].between("2025-11-01", "2025-11-30 23:59:59")]

Filtering on text

Text columns have a .str accessor with vectorised string methods that return masks:

products["name"].str.contains("Lamp")              # name includes 'Lamp'
products["name"].str.contains("lamp", case=False)  # ignore case
products["name"].str.startswith("Oak")
products["subcategory"].isin(["Pendants", "Chandeliers"])

So “every product with Brass in the name” is products[products["name"].str.contains("Brass")].

Two cautions with str.contains:

• It treats the pattern as a regular expression by default, so characters like (, . and + have special meanings. Pass regex=False to match text literally.
• On a column with missing values, it returns NaN for those rows, and using that as a mask fails. Pass na=False to treat missing text as “doesn’t contain”.

Building the answer

mask = (products["category"] == "Lighting") & products["unit_price"].between(50, 200)
(
    products.loc[mask, ["name", "unit_price"]]
    .sort_values(["unit_price", "name"])
    .reset_index(drop=True)
)

sort_values with a list sorts ascending on every column by default, which is what this brief wants.

The price is a snapshot

products.unit_price is the current list price. Some products had a price rise in March 2025, so older order lines in order_items show a lower price paid. For a campaign list, the current price is right. For revenue, always use the price on the order line. Picking the right column for the question is part of the job.

Check the edges

After filtering a range, look at the smallest and largest values that made it through: result["unit_price"].agg(["min", "max"]). If the brief says $50 to $200 and the minimum is $54.99, check whether a product at exactly $50 exists and was wrongly excluded. Edge checks like this take seconds and catch the inclusive/exclusive mistakes that reviewers love to find.

Common mistakes

• Using between when the brief says “under” and including the upper bound.
• Forgetting na=False on str.contains for a column with gaps.
• Searching with the wrong case: str.contains("lamp") misses “Floor Lamp”.