Python/sorts/quick_sort.py

"""
This is a pure python implementation of the quick sort algorithm

For doctests run following command:
python -m doctest -v quick_sort.py
or
python3 -m doctest -v quick_sort.py

For manual testing run:
python quick_sort.py
"""
from __future__ import print_function
from random import shuffle


def sort(collection):
    shuffle(collection)
    return quick_sort(collection)


def quick_sort(collection):
    """Pure implementation of quick sort algorithm in Python

    :param collection: some mutable ordered collection with heterogeneous
    comparable items inside
    :return: the same collection ordered by ascending

    Examples:
    >>> quick_sort([0, 5, 3, 2, 2])
    [0, 2, 2, 3, 5]

    >>> quick_sort([])
    []

    >>> quick_sort([-2, -5, -45])
    [-45, -5, -2]
    """
    if len(collection) <= 1:
        return collection
    less = []
    equal = []
    greater = []
    pivot = collection[0]
    for x in collection:
        if x < pivot:
            less.append(x)
        elif x == pivot:
            equal.append(x)
        else:
            greater.append(x)
    return quick_sort(less) + equal + quick_sort(greater)


if __name__ == '__main__':
    import sys

    # For python 2.x and 3.x compatibility: 3.x has not raw_input builtin
    # otherwise 2.x's input builtin function is too "smart"
    if sys.version_info.major < 3:
        input_function = raw_input
    else:
        input_function = input

    user_input = input_function('Enter numbers separated by a comma:\n')
    unsorted = [int(item) for item in user_input.split(',')]
    print(sort(unsorted))