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:

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]
                 

2. imap:

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)
                    else:
                     yield function(*args)
                 
                  >>> [ j for j in i.imap(lambda x,y:x+y,[1,2,3],[4,5,6])]
                  [5, 7, 9]
                 

3. islice:

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]
                 

4. izip:

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)]