decorate-sort-undecorate design pattern python' support for key function when sorting is implemented using what is known as the decorate-sort-undecorate design pattern it proceeds in steps each element of the list is temporarily replaced with "decoratedversion that includes the result of the key function applied to the element the list is sorted based upon the natural order of the keys (figure the decorated elements are replaced by the original elements red blue cyan green magenta yellow figure list of "decoratedstringsusing their lengths as decoration this list has been sorted by those keys although there is already built-in support for pythonif we were to implement such strategy ourselvesa natural way to represent "decoratedelement is using the same composition strategy that we used for representing key-value pairs within priority queue code fragment of section includes just such an item classdefined so that the operator for items relies upon the given keys with such compositionwe could trivially adapt any sorting algorithm to use the decoratesort-undecorate patternas demonstrated in code fragment with merge-sort def decorated merge sort(datakey=none) """demonstration of the decorate-sort-undecorate pattern "" if key is not none for in range(len(data))decorate each element data[jitem(key(data[ ])data[ ] merge sort(datasort with existing algorithm if key is not none for in range(len(data))undecorate each element data[jdata[jvalue code fragment an approach for implementing the decorate-sort-undecorate pattern based upon the array-based merge-sort of code fragment the item class is identical to that which was used in the priorityqueuebase class (see code fragment