Python - Itertools Part 2

Today I am going to explain my understanding on some of the amazing functions available in python's itertools module. These too are very essential functions, and a clear understanding of these methods would help one in becoming a better python programmer. All these methods will return an iterable object as response.

  1. ifilterfalse:
  2. Returns only those for which the predicate is False. If predicate is None, return the items that are false.

                      def ifilterfalse(predicate, iterable):
                       if predicate is None:
                        predicate = bool
                       for x in iterable:
                        if not predicate(x):
                         yield x
                      >>> [j for j in i.ifilterfalse(lambda x:x%5,range(30))]
                      [0, 5, 10, 15, 20, 25]
  3. imap:
  4. Maps the list of elements to a function and provide the applied result. This method can accept several lists as arguments depending on the target function's arguments.

                      def imap(function, *iterables):
                       # imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000
                       iterables = map(iter, iterables)
                       while True:
                        args = [next(it) for it in iterables]
                        if function is None:
                         yield tuple(args)
                         yield function(*args)
                      >>> [ j for j in i.imap(lambda x,y:x+y,[1,2,3],[4,5,6])]
                      [5, 7, 9]
  5. islice:
  6. Accepts 3 argumenst namely start,stop and the iterator and returns a subset of the list.This is similar to substr and normal index slicing.

                      >>> [j for j in i.islice([1,2,3,4,5],2,4)]
                      [3, 4]
  7. izip:
  8. This method maps the given two lists(iterables) and returns a tuple.

                      >>> [j for j in i.izip(range(4),range(5,11))]
                      [(0, 5), (1, 6), (2, 7), (3, 8)]

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