P6.4 How to Build a New List Inside a Loop

By Ravindra Bagale, trainer LinkedIn Last updated: 27 October 2026

Why. Often you transform data: convert all prices, keep only some rows. You collect results into a new list.

What. Start with an empty list [], then append inside the loop.

How.

Collect results

Worked example A — Convert dollars to rupees.

Step 1 — What we do. Prices in USD for an IT company; rate ₹83 per $.

Step 2 — Type and run this code.

usd = [10, 25, 40]
inr = []
for p in usd:
    inr.append(p * 83)
print(inr)

Step 3 — Output you should see.

[830, 2075, 3320]

Step 4 — What it means. Each converted price is added to the new list.

Worked example B — Keep only some items.

Step 1 — What we do. We keep only orders above ₹500.

Step 2 — Type and run this code.

orders = [250, 800, 1200, 300, 650]
big = []
for o in orders:
    if o > 500:
        big.append(o)
print(big)

Step 3 — Output you should see.

[800, 1200, 650]

Step 4 — What it means. This is filtering. In pandas, df[df.amount > 500] does the same.

Ravindra Bagale's Tip

Do not change a list while looping over it. Build a new list instead.