Fixed typos and added the shell sort algorithm

sorts/shell_sort.py

@@ -0,0 +1,58 @@
+"""
+This is a pure python implementation of the shell sort algorithm
+
+For doctests run following command:
+python -m doctest -v shell_sort.py
+or
+python3 -m doctest -v shell_sort.py
+
+For manual testing run:
+python shell_sort.py
+"""
+from __future__ import print_function
+
+
+def shell_sort(collection):
+    """Pure implementation of shell sort algorithm in Python
+    :param collection:  Some mutable ordered collection with heterogeneous
+    comparable items inside
+    :return:  the same collection ordered by ascending
+    
+    >>> shell_sort([0, 5, 3, 2, 2)]
+    [0, 2, 2, 3, 5]
+
+    >>> shell_sort([])
+    []
+     
+    >>> shell_sort([-2, -5, -45]) 
+    [-45, -5, -2]
+    """
+    # Marcin Ciura's gap sequence
+    gaps = [701, 301, 132, 57, 23, 10, 4, 1]
+    
+    for gap in gaps:
+        i = gap
+        while i < len(collection):
+            temp = collection[i]
+            j = i
+            while j >= gap and collection[j-gap] > temp:
+                collection[j] = collection[j - gap]
+                j -= gap
+            collection[j] = temp
+            i += 1
+        
+        
+    return collection
+
+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(shell_sort(unsorted))