If L is a list with 6 elements, then which of the following statements will raise an exception ?
If L is a list with 6 elements, then which of the following statements will raise an exception ?
Options
Option B — L.pop(6) raises an exception, because a list L with 6 elements has valid indices only from 0 to 5; index 6 is out of range for pop().
Marking Scheme
- 11 mark: for correctly selecting option B.
Hint
pop() needs a valid EXISTING index and raises IndexError if out of range; insert() never raises IndexError — it just clamps to a valid position.
Quick Oral Answer
L.pop(6) raises an exception because a 6-element list only has valid indices 0 to 5; insert(), unlike pop(), never raises IndexError since it clamps out-of-range indices to the end of the list.
Analysis & Explanation
This question tests the boundary behaviour of list methods pop() and insert(), which behave differently when given an out-of-range index.
Concept
- For a list L with 6 elements, valid (0-based) indices are 0, 1, 2, 3, 4, 5.
pop(index)REMOVES and returns the element at that index — it strictly requires a valid existing index, else it raisesIndexError: pop index out of range.insert(index, value)INSERTS a new value at that position — it never raises an error for out-of-range indices; if the index exceeds the list's length, Python simply inserts the value at the end.
Option-by-option check
- A:
L.pop(1)— index 1 is valid (0 to 5); works fine. - B:
L.pop(6)— index 6 does NOT exist (max valid index is 5); raisesIndexError. This is the correct answer. - C:
L.insert(1,6)— inserts value 6 at index 1; valid, no error. - D:
L.insert(6,1)— index 6 is beyond the last valid index, but insert() clamps out-of-range indices and simply appends the value at the end; no error.
Exam trap
- Students often assume insert() will also raise an error like pop() for an out-of-range index — but insert() is designed to be error-tolerant and always succeeds by clamping to the nearest valid position.
Common Mistakes
- 1Assuming insert() behaves like pop() and raises an error for out-of-range indices.
- 2Forgetting that valid indices for a 6-element list only go up to 5, not 6.
Interesting Facts
insert() with an index far beyond the list length (e.g., L.insert(100, 'x')) still works without error — it just appends the value at the very end.
pop() with no argument at all removes and returns the LAST element of the list, equivalent to pop(-1).
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Frequently Asked Questions
Does insert() ever raise an IndexError in Python?
No. insert() never raises an IndexError for out-of-range indices — if the given index exceeds the list length, the value is simply inserted (appended) at the end of the list.
What error does pop() raise for an invalid index?
It raises `IndexError: pop index out of range` when the given index does not correspond to an existing element in the list.