Iterator Functions in Python | Set 2 (islice (), starmap (), tee () ..)

1. islice (iterable, start, stop, step) : — this iterator selectively prints the values ​​referenced in its iterable container passed as an argument. This iterator takes 4 arguments, an iterative container, start position, end position, and stride.

2. starmap (func., List of tuples) : — This iterator takes a function and a list of tuples as an argument and returns a value according to the function from each tuple in the list.

# Python code to demonstrate how it works # islice () and starmap ()   # import & quot; itertools & quot; for iterator operations import itertools   # initializing list li = [ 2 , 4 , 5 , 7 , 8 , 10 , 20 ]    # initialize the list of tuples li1 = [( 1 , 10 , 5 ), ( 8 , 4 , 1 ), ( 5 , 4 , 9 ), ( 11 , 10 , 1 )]       # using islice () to slice the list according to ... need # starts printing from 2nd index to 6th skip 2 print ( "The sliced ​​list values ​​are:" , end = "") print ( list (itertools.islice (li, 1 , 6 , 2 )))   # using starmap () to select a value acc. function # selects the minimum of all tuple values ​​ print ( "The values ​​acc. to function are:" , end = "") print ( list (itertools.starmap ( min , li1)))

Output:

 The sliced ​​list values ​​are: [4, 7, 10] The values ​​acc. to function are: [1, 1, 4, 1] 

3. takewhile (func, iterable) : — this iterator is the opposite of drop while (), it prints the values ​​ until the function returns false the first time.

4. tee (iterator, count) : — This iterator splits the container into multiple iterators mentioned in the argument.

# Python code to demonstrate how it works # takewhile () and tee ()   # import & quot; itertools & quot; for iterator operations import itertools   # initializing list li = [ 2 , 4 , 6 , 7 , 8 , 10 , 20 ]    # save the list in an iterator iti = iter (li)    # using takewhile () to print values ​​until the condition is false. print ( " The list values ​​till 1st false value are: " , end = " ") print ( list (itertools.takewhile ( lambda x: x % 2 = = 0 , li)))   # using tee () to list iterators # makes a list of 3 iterators that have the same value. it = itertools.tee (iti, 3 )   # printing iterator values ​​ print ( "The iterators are:" ) for i in range ( 0 , 3 ): print ( list (it [i]))

Output:

 The list values ​​till 1st false value are : [2, 4, 6] The iterators are: [2, 4, 6, 7, 8, 10, 20] [2, 4, 6, 7, 8, 10, 20] [2, 4, 6, 7 , 8, 10, 20] 

5. zip_longest (iterable1, iterable2, fillval.) : — this iterator prints the values ​​of the iterables one at a time . If one of the iterations is printed completely, the remaining values ​​are filled with the values ​​assigned to fillvalue .

# Python code to demonstrate how it works # zip_longest ()   # import & quot; itertools & quot; for iterator operations import itertools   # using zip_longest () to combine the two iterations. print ( "The combined values ​​of iterables is :" ) print ( * (itertools.zip_longest ( ’GesoGes’ , ’ ekfrek’ , fillvalue = ’_’ )))

Output:

 The combined values ​​of iterables is: (’G’,’ e’) (’e’,’ k’) (’s’,’ f’) (’o’,’ r ’) (’ G’, ’e’) (’ e’, ’k’) (’ s’, ’_’) 

Combinatorial iterators

1. product (iter1, iter2) : — This iterator prints the Cartesian product of the two iterable containers passed as arguments.

2. permutations (iter, group_size) : — this iterator prints all possible permutations of all elements of the iterable.  The size of each permutation group is determined by the group_size argument.

# Python- demo code # product () and permutation ()   # import & quot; itertools & quot; for iterator operations import itertools   # using product () to print a Cartesian product print ( "The cartesian product of the containers is:" ) print ( list (itertools.product ( ’AB’ , ’ 12’ )))   # use permutations to compute all possible permutations print ( "All the permutations of the given container is:"  ) print ( list (itertools.permutations ( ’GfG’ , 2 )))

Output:

 The cartesian product of the containers is: [(’A’, ’1’), (’ A’, ’2’), (’ B’, ’1’), (’ B’, ’2’)] All the permutations of the given container is: [(’ G’, ’f’), (’ G’, ’G’), (’ f’, ’G’), (’ f’, ’G’), (’ G’, ’G’), (’ G’, ’f’)] 

3. combinations (iterable, group_size) : — this iterator prints all possible combinations (no replacement) of the container passed in arguments in the specified group size in sorted order.

4. combinations_with_replacement (iterable, group_size) : — this iterator prints all possible combinations (with replacement) of the container passed in arguments in the specified group size in sorted order.

# Python code to demonstrate how it works # combination () and combination_with_replacement ()   # import & quot; itertools & quot; for iterator operations import itertools   # use combinations () to print each combination # (without replacements) print ( "All the combination of container in sorted order (without replacement) is: " ) print ( list (itertools.combinations ( ’1234’ , 2 )))   # using combination_with_replacement () to print each combination # with replacement print ( "All the combination of container in sorted order (with replacement) is:" ) print ( list (itertools.combinations_with_replacement ( ’GfG’ , 2 )))

Output:

 All the combination of container in sorted order (without replacement) is: [(’1’,’ 2 ’), (’ 1’, ’3’), (’ 1’, ’4’), (’ 2’, ’3’), (’ 2’, ’4’), (’ 3’, ’4 ’)] All the combination of container in sorted order (with replacement) is: [(’ G’, ’G’), (’ G’, ’f’), (’ G’, ’G’), (’ f’, ’f’), (’ f’, ’G’), (’ G’, ’G’)] 

Infinite iterators

1. count (start, step) : — This iterator starts printing at "start" and prints indefinitely . If steps are mentioned, numbers are skipped, otherwise step is 1 by default.

Example:

 iterator.count (5,2) prints - 5,7,9,11 .. .infinitely 

2. loop (iterable) : — this iterator prints all values ​​in order from the passed container. It resumes printing from the beginning again when all items are cycled .

Example:

 iterator.cycle ([1,2,3,4]) prints - 1,2,3,4,1,2,3,4,1 ... infinitely 

3. repeat (val, num) : — This iterator repeatedly prints the passed value an infinite number of times. If a number is mentioned, they are up to that number.

# Python code to demonstrate how it works # repeat ()   # import & quot; itertools & quot; for iterator operations import itertools   # using repeat () to repeatedly print the number print ( "Printing the numbers repeatedly:" ) print ( list (itertools.repeat ( 25 , 4 )))

Output:

 Printing the numbers repeatedly: [25, 25, 25, 25] 

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