Selection Sort—Python

Selection sorts are a very common method of sorting. Here is a selection sort that is implemented in Python.

def selection_sort(items):
    for i in range(len(items) - 1):
        # Assume that the smallest item is located at index i
        smallest = i

        # Now loop through the rest of the list
        for j in range(i + 1, len(items)):
            # Is our item at index j smaller than our smallest item?
            if items[j] < items[smallest]:
                smallest = j

        #  Now swap elements to perform the sort
        temp = items[smallest]
        items[smallest] = items[i]
        items[i] = temp

if __name__ == '__main__':
    items = ['Bob Belcher', 'Linda Belcher', 'Gene Belcher', 'Tina Belcher', 'Louise Belcher']
    print(items, '\n')

    print('Sorting...')
    selection_sort(items)
    print(items)

Selection sorts use nested loops to iterate over a list. We check if the item at index j is less than the current smallest item. If j is smaller than smaller, we assign smaller to j.

Once we complete the nested loop, we can perform a swap. Our driver program demonstrates this with strings, but thanks to Python's duck typing system, this will sort any object that implements __lt__.

When run, we get this output

['Bob Belcher', 'Linda Belcher', 'Gene Belcher', 'Tina Belcher', 'Louise Belcher'] 

Sorting...
['Bob Belcher', 'Gene Belcher', 'Linda Belcher', 'Louise Belcher', 'Tina Belcher']

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