Tighten up quicksort()

DIRECTORY.md

@@ -738,6 +738,7 @@
   * [Iterative Merge Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/iterative_merge_sort.py)
   * [Merge Insertion Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/merge_insertion_sort.py)
   * [Merge Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/merge_sort.py)
+  * [Natural Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/natural_sort.py)
   * [Odd Even Transposition Parallel](https://github.com/TheAlgorithms/Python/blob/master/sorts/odd_even_transposition_parallel.py)
   * [Odd Even Transposition Single Threaded](https://github.com/TheAlgorithms/Python/blob/master/sorts/odd_even_transposition_single_threaded.py)
   * [Pancake Sort](https://github.com/TheAlgorithms/Python/blob/master/sorts/pancake_sort.py)

sorts/quick_sort.py

@@ -1,48 +1,36 @@
 """
-This is a pure Python implementation of the quick sort algorithm
+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
+python3 quick_sort.py
 """
 
 
-def quick_sort(collection):
-    """Pure implementation of quick sort algorithm in Python
+def quick_sort(collection: list) -> list:
+    """A pure Python implementation of quick sort algorithm
 
-    :param collection: some mutable ordered collection with heterogeneous
-    comparable items inside
+    :param collection: a mutable collection of comparable items
     :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]
+    >>> quick_sort([-2, 5, 0, -45])
+    [-45, -2, 0, 5]
     """
-    length = len(collection)
-    if length <= 1:
+    if len(collection) < 2:
         return collection
-    else:
-        # Use the last element as the first pivot
-        pivot = collection.pop()
-        # Put elements greater than pivot in greater list
-        # Put elements lesser than pivot in lesser list
-        greater, lesser = [], []
-        for element in collection:
-            if element > pivot:
-                greater.append(element)
-            else:
-                lesser.append(element)
-        return quick_sort(lesser) + [pivot] + quick_sort(greater)
+    pivot = collection.pop()  # Use the last element as the first pivot
+    greater = []  # All elements greater than pivot
+    lesser = []  # All elements less than or equal to pivot
+    for element in collection:
+        (greater if element > pivot else lesser).append(element)
+    return quick_sort(lesser) + [pivot] + quick_sort(greater)
 
 
 if __name__ == "__main__":