Basic example
Input
most_common_item([1, 2, 2, 3])
Output
2
2 appears twice, more than any other item.
Full lesson preview
Build a frequency dictionary and return the most common item
Count how often items appear and return the most frequent one, with a clear tie-breaker.
Python practice24 minDictionaries & SetsAdvancedLast updated March 18, 2026
Problem statement
Write a function most_common_item(items) that takes an iterable (like a list or tuple) of hashable items and returns the item that occurs most frequently. If the iterable is empty, return None. If two or more items have the same highest frequency, return the item among them that appears earliest in the original iterable. Do not use collections.Counter; implement the counting and tie-breaking logic yourself.
Task
Given an iterable of hashable items, build a frequency mapping and return the item with the highest frequency. If multiple items tie, return the one that appears first in the input.
Examples
Input format
A single iterable value (e.g., a list) passed as the argument to most_common_item.
Output format
Return the most common item (any hashable type). If input is empty, return None.
Constraints
- Items are hashable (can be used as dictionary keys).
- The input may be large but fits in memory.
- Do not use collections.Counter; build the frequency mapping manually.
Samples
Sample 1
Input
most_common_item(['a', 'b', 'a', 'c', 'b', 'a'])
Output
a
a appears 3 times, more than any other item.