Insertion and Quick Sort - No explanation.

import sys
import random

def insertion_sort(a):
    """ Returns the sorted version of 'a'
    """

    for i, _ in enumerate(a):
        for j in range(i):
            if a[i] < a[j]:
                a[i], a[j] = a[j], a[i]

    return a
            
def quick_sort(a):
    """ Returns the sorted version of 'a'

    Quick sort - find a pivot element and return
        quick-sorted elements less than pivot +
        pivot +
        quick-sorted elements greater than pivot.
    *** Following implementation is not optimal in space ***
    """

    if len(a) <= 0:
        return a

    # use first element as pivot - not so superior, but doesn't matter.
    pivot = a[0]
    left = [x for x in a[1:] if x <= pivot]
    right = [x for x in a[1:] if x > pivot]
    
    return quick_sort(left) + [pivot] + quick_sort(right)

def quick_sort_helper(a, _min, _max):

    if _max <= _min:
        return a

    # pick a random pivot element
    _piv = partition(a, _min, _max)
    quick_sort_helper(a, _min, _piv-1)
    quick_sort_helper(a, _piv+1, _max)
    return a

def partition(a, _min, _max):
    """
    1. Put the pivot in its position
    2. Partition the array in place so that all elements less than pivot
    are arranged to left of it and vice-versa
    
    """
    _piv = random.randint(_min, _max)
    pivot = a[_piv]
    
    i = _min+1 # pivot will be put in first position
    j = _max

    a[_piv], a[_min] = a[_min], a[_piv]
    while True:
        while (i <= j) and (a[i] <= pivot):
            i += 1
        while (j >= i) and (a[j] > pivot):
            j -= 1
        if i < j:
            a[i], a[j] = a[j], a[i]
        else:
            break

    a[_min], a[j] = a[j], a[_min]
    return j

def quick_sort_opt(a):
    """ Returns the sorted version of 'a'
    Space efficient.
    """

    if len(a) <= 0:
        return a

    return quick_sort_helper(a, 0, len(a)-1)

if __name__ == "__main__":
    print(insertion_sort([4, 3, 2, 1]))
    print(insertion_sort([10,3,6,1,2,-4,7,23,22,21]))
    print(insertion_sort(list('INSERTIONSORT')))
    print(quick_sort([4, 3, 2, 1]))
    print(quick_sort(list('insertionsort')))
    print(partition([4,3,2,1], 0, 3))
    print(partition([6, 8, 6, 7, 2, 3], 0, 5))
    print(quick_sort_opt([4, 3, 2, 1]))
    print(quick_sort_opt(list('insertionsort')))
    print(quick_sort_opt([6, 8, 6, 7, 2, 3]))
    print(quick_sort_opt([2]*8))
    print("In main - Hello world!")