Is this a proper quicksort algorithm in Python?

import random

def qsort(qslist):

    small = []
    big = []

    if (len(qslist)  1):

        pivot = qslist[int(random.randrange(len(qslist)))]

        for x in range(len(qslist)):
            if qslist[x] <= pivot:
                small.append(qslist[x])
            else:
                big.append(qslist[x])
        if(len(big) == 0):
            big.append(pivot)
            small.remove(pivot)

return qsort(small) + qsort(big)

qslist = [9,1,8,2,7,3,6,4,5]
print(qsort(qslist))

Please give me advice while picking up Python. I'm trying to do so while at the same time doing some basic algorithms.

• Have I understood how the quicksort algorithm work?

• Please give me some general feedback on the Python code.

Some comments:

• Write docstrings to document code

• Use if/else instead of if/elif if possible

• Use list comprehensions

• Use random.choice to get a random element from a non-empty sequence

The code in the original questions with the suggested improvements would be as follows:

import random

def qsort(qslist):
    """"Quicksort implementation."""
    if len(qslist)  pivot]

    return qsort(small) + equal + qsort(big)

qslist = [9,1,8,2,7,3,6,4,5]
print(qsort(qslist))

Edit: If you prefer to avoid traversing the array three times, a partition
function to do that very similar to the one in the original question would be:

def partition(qslist):
    """Partition array using a pivot value."""
    small = []
    equal = []
    big = []

    pivot = random.choice(qslist)
    for x in qslist:
        if x < pivot:
            small.append(x)
        elif x == pivot:
            equal.append(x)
        else:
            big.append(x)

    return small, equal, big

StackExchange Code Review Q#59229, answer score: 2