Python Lists: Filter Values with Explicit Loops

An inventory list includes quantities, but a report needs only low-stock items.

What You Need to Understand

An explicit for loop with an if statement can filter a list into a new list. This is easy to read and debug when you are first learning iteration.

When to Use It

An inventory list includes quantities, but a report needs only low-stock items.

Step-by-Step Python Example

quantities = [5, 0, 13, 2, 0]
low_stock = []
for quantity in quantities:
    if quantity < 3:
        low_stock.append(quantity)
print(low_stock)

How the Example Works

The loop evaluates every quantity and retains those below three; the source list remains unchanged.

Example Output

[0, 2, 0]
['Daniel']

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

names = ["Al", "Maya", "Daniel"]
print([name for name in names if len(name) >= 5])

Important Behavior and Edge Cases

Do not change the same list you are iterating over when removing unwanted items; build a result list instead.

Try It Yourself

Filter all names whose length is at least five characters.

Common Beginner Mistakes

Do not change the same list you are iterating over when removing unwanted items; build a result list instead.
Overlooking how an iterable is consumed, how element positions are chosen, or whether a function creates a new list.

Key Takeaways

An explicit for loop with an if statement can filter a list into a new list.
The loop evaluates every quantity and retains those below three; the source list remains unchanged.
Do not change the same list you are iterating over when removing unwanted items; build a result list instead.