Count frequency of items in a list

frequency_counter.py

from collections import defaultdict, Counter

import random

# using the dictionary data structure
def frequency_counter(li):
    freq_dt = dict()
    for item in li:
        if item in freq_dt:
            freq_dt[item] += 1
        else:
            freq_dt[item] = 1

    return freq_dt


# using defaultdict
def frequency_counter(li):
    freq_dt = defaultdict(int)
    for item in li:
        freq_dt[item] += 1

    return freq_dt


# using Counter
def frequency_counter(li):
    freq_dt = Counter(li)
    return freq_dt


if __name__ == "__main__":
    li = [2, 6, 9, 2, 8, 2, 9, 9, 3, 1, 4, 5, 7, 1, 8, 10, 2, 10, 10, 5]
    freq = frequency_counter(li)
    assert freq[1] == 2
    assert freq[2] == 4
    assert freq[3] == 1
    assert freq[11] == 0 # this test will fail when we use dictionary (the first function)