PCEP Computer Programming and Python Fundamentals Practice Question

A junior developer is writing a script to process a list of user IDs: ids = [101, 102, 103, 104]. The goal is to create a new list where each ID is increased by 10, without modifying the original list. The developer writes: new_ids = ids.append(10). However, the output shows None. The developer needs to correctly create the new list. Which code should the developer use to achieve this?

⚠ Common exam trap

Python Institute often tests the distinction between methods that modify a list in place and return `None` (like `append()`, `sort()`) versus those that return a new object (like list comprehensions or `sorted()`), leading candidates to mistakenly assign the result of `append()` to a variable.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

new_ids = [id + 10 for id in ids]

It uses a list comprehension to create a new list by adding 10 to each element of the original list `ids`, leaving the original list unchanged. The `append()` method modifies the list in place and returns `None`, which is why the developer got `None`.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
new_ids = [id + 10 for id in ids]
Why this is correct
List comprehension creates a new list with increments, original unchanged.
✗
for i in range(len(ids)): ids[i] += 10; new_ids = ids
Why it's wrong here
Modifies the original list, so original ids are changed.
✗
new_ids = ids + 10
Why it's wrong here
Cannot concatenate list and int; TypeError.
✗
new_ids = map(lambda x: x+10, ids)
Why it's wrong here
map returns an iterator, not a list. Needs list() conversion.

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PCEP Computer Programming and Python Fundamentals Practice Question

Why each option matters

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