data structuresalgorithmsand code simplification heappushpop(heapitemadds item to the heap and removes the smallest item from heap in single operation this is more efficient than calling heappush(and heappop(separately heapreplace(heapitemreturns and removes the smallest item from the heap at the same timea new item is added the heap condition is preserved in the process this function is more efficient than calling heappop(and heappush(in sequence in additionthe returned value is obtained prior to adding the new item thereforethe return value could be larger than item raises indexerror if heap is empty merge( creates an iterator that merges the sorted iterables and so on into single sorted sequence this function does not consume the inputs but returns an iterator that incrementally processes the data nlargest(niterable [key]creates list consisting of the largest items in iterable the largest item appears first in the returned list key is an optional function that takes single input parameter and computes the comparison key for each item in iterable nsmallest(niterable [key]creates list consisting of the smallest items in iterable the smallest item appears first in the returned list key is an optional key function note the theory and implementation of heap queues can be found in most books on algorithms itertools the itertools module contains functions for creating efficient iteratorsuseful for looping over data in various ways all the functions in this module return iterators that can be used with the for statement and other functions involving iterators such as generators and generator expressions chain(iter iter iterngiven group of iterators (iter itern)this function creates new iterator that chains all the iterators together the returned iterator produces items from iter until it is exhausted then items from iter are produced this continues until all the items in itern are exhausted chain from_iterable(iterablesan alternative constructor for chain where the iterables is an iterable that produces sequence of iterable objects the result of this operation is the same as what would be produced by the following fragment of generator codef lib fl ff