List length
Input
seq_length([1, 2, 3])
Output
3
The list has three elements.
Full lesson preview
Write a function that returns the length of a sequence
Implement a function that returns the length (number of items) of any iterable or sequence.
Python practice8 minFunctions & ScopeBeginnerLast updated March 17, 2026
Problem statement
Write a function seq_length(seq) that returns the number of items in seq. If seq supports len(seq), use that. If not (for example, a generator), iterate through the iterable and count items. The function should not modify the iterable beyond consuming it when necessary.
Task
Create seq_length(seq) to return how many items are in seq. Support sequences (with len) and general iterables (by iterating).
Examples
Input format
One argument: any sequence or iterable.
Output format
An integer representing the number of items.
Constraints
Do not assume all inputs support len(). If len() raises TypeError, count by iterating.
Samples
Sample 1
Input
seq_length('hello')
Output
5
Strings support len(), returning 5.