Python - Itertools Part 1

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. count:

A count method is similar to range and xrange methods,except the fact that it does'nt need a stop variable. The implementation is shown below,

             def count(start=0, step=1):
              # count(10) --> 10 11 12 13 14 ...
              # count(2.5, 0.5) -> 2.5 3.0 3.5 ...
              n = start
              while True:
               yield n
               n += step
              >>> li=[1,2,3]
              >>> map(lambda x:x**2,li)
              [1, 4, 9]
            

2. reduce:

A cycle method loops over the given list of items again and again.

           
            def cycle(iterable):
             # cycle('ABCD') --> A B C D A B C D A B C D ...
             saved = []
             for element in iterable:
              yield element
              saved.append(element)
             while saved:
              for element in saved:
                 yield element
               

3. dropwhile:

Make an iterator that drops elements from the iterable as long as the predicate is true; afterwards, returns every element.

                 for j in i.dropwhile(lambda x: x<5, [1,4,6,4,1]):
                     print j
           
            6
            4
            1
           

Here, 1,4 fails the test and once 6 passes,all other elements are returned.
4. ifilter:

this method filters the data such that the data that pass validation are returned as result.

            >>> for j in i.ifilter(lambda x: x%2, range(10)):
             j
           
           
            1
            3
            5
            7
            9